Supplement to Definitive Proxy Statement (Form 8-K)

The purpose of the Special Meeting is to consider and vote on a proposal to adopt the Agreement and Plan of Merger and Combination, dated as of July 12, 2021 (the "Merger Agreement"), by and among STFC, State Automobile Mutual Insurance Company, an Ohio mutual insurance company ("SAM"), Liberty Mutual Holding Company Inc., a Massachusetts mutual holding company ("LMHC"), Pymatuning, Inc., an Ohio corporation and wholly-owned indirect subsidiary of LMHC ("Merger Sub I"), and Andover, Inc., an Ohio corporation and wholly-owned direct subsidiary of LMHC (the "Merger Proposal"). Pursuant to the terms of the Merger Agreement, among other things, Merger Sub I will be merged with and into STFC (the "Merger"), the separate corporate existence of Merger Sub I will cease and STFC will continue as the surviving entity. The Definitive Proxy Statement is amended and supplemented by, and should be read as part of, and in conjunction with, the information set forth in this Current Report on Form 8-K. To the extent that information set forth herein differs from or updates information contained in the Definitive Proxy Statement, the information contained herein supersedes the information contained in the Definitive Proxy Statement. Capitalized terms used but not defined herein have the meanings set forth in the Definitive Proxy Statement.

If any shareholders have not already submitted a proxy for use at the Special Meeting, they are urged to do so promptly. No action in connection with the information set forth in this Current Report on Form 8-K is required by any shareholder who has previously delivered a proxy and who does not wish to revoke or change that proxy.

If you have any questions concerning the Merger Agreement, the Merger, the Special Meeting or the Definitive Proxy Statement, would like additional copies of the Definitive Proxy Statement, or need help submitting a proxy to have your shares voted, please contact STFC Investor Relations at (800) 622-6757 (U.S., Canada, Puerto Rico) or (781) 575-4735 (outside the U.S.).

STFC believes that the Definitive Proxy Statement contains all material information required to be disclosed. However, STFC wishes to voluntarily make supplemental disclosures related to the Merger, which are set forth below. Nothing in this Current Report on Form 8-K shall be deemed an admission of the legal necessity or materiality under applicable law of any of the disclosures set forth herein. STFC specifically denies that any further disclosure is required to supplement the disclosure set forth in the Definitive Proxy Statement under applicable law.

The information contained herein speaks only as of September 28, 2021, unless the information specifically indicates that another date applies.

Unaudited Financial Projections of the Company.

Opinion of Houlihan Lokey Capital, Inc. - Financial Analyses.

Opinion of Houlihan Lokey Capital, Inc. - Other Matters.

Houlihan Lokey and certain of its affiliates may provide investment banking, financial advisory and/or other financial or consulting services to the Company, SAM, LMHC, other participants in the Transactions or certain of their respective affiliates or security holders in the future, for which Houlihan Lokey and its affiliates may receive compensation. Furthermore, in connection with bankruptcies, restructurings, distressed situations and similar matters, Houlihan Lokey and certain of its affiliates may have in the past acted, may currently be acting and may in the future act as financial advisor to debtors, creditors, equity holders, trustees, agents and other interested parties (including, without limitation, formal and informal committees or groups of creditors) that may have included or represented and may include or represent, directly or indirectly, or may be or have been adverse to, the Company, SAM, LMHC, other participants in the Transactions or certain of their respective affiliates or security holders, for which advice and services Houlihan Lokey and its affiliates have received and may receive compensation.Based on a review of its internal information management systems, Houlihan Lokey did not identify any engagements by the Company, SAM or LMHC for which Houlihan Lokey received fees for providing investment banking or financial advisory services during the two years immediately prior to the date of its opinion.

Cautionary Notice Regarding Forward-Looking Statements

Except for historical information, all other information in this communication consists of forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements, and related oral statements STFC may make, are subject to risks and uncertainties that could cause actual results to differ materially from those projected, anticipated or implied. For example, (1) conditions to the closing of the transactions may not be satisfied; (2) regulatory approvals required for the transactions may not be obtained, or required regulatory approvals may delay the transactions or result in the imposition of conditions that could have a material adverse effect on LMHC, SAM or STFC or cause the parties to abandon the transactions; (3) uncertainty as to the timing of completion of the transactions; (4) the business of LMHC, SAM or STFC may suffer as a result of uncertainty surrounding the transactions; (5) the occurrence of any event, change or other circumstances that could give rise to the termination of the Merger Agreement; (6) risks related to disruption of management's attention from the ongoing business operations of LMHC, SAM or STFC due to the transactions; (7) the effect of the announcement of the transactions on the relationships of LMHC, SAM or STFC with its clients, operating results and business generally; (8) the outcome of any legal proceedings to the extent initiated against LMHC, SAM or STFC following the announcement of the proposed transaction; and (9) LMHC, SAM or STFC may be adversely affected by other economic, business, and/or competitive factors as well as management's response to any of the aforementioned factors. The foregoing review of important factors should not be construed as exhaustive and should be read in conjunction with the other cautionary statements that are included herein and elsewhere, including the risk factors included in STFC's most recent Annual Report on Form 10-K, STFC's most recent Quarterly Report on Form 10-Q, the Definitive Proxy Statement and other documents of STFC on file with the SEC. STFC undertakes no obligation to update or revise any forward-looking statements.

Additional Information and Where to Find It

In connection with the proposed transaction, STFC has filed with the SEC the Definitive Proxy Statement and may file or furnish other documents with the SEC regarding the proposed transaction. This communication is not a substitute for the Definitive Proxy Statement or any other document that STFC may file with the SEC. TheDefinitive Proxy Statement was filed with the SEC and was first mailed to shareholders of STFC on August 27, 2021. INVESTORS IN AND SECURITY HOLDERS OF STFC ARE URGED TO READ THEDEFINITIVE PROXY STATEMENT AND ANY OTHER RELEVANT DOCUMENTS THAT ARE FILED WITH OR FURNISHED TO OR WILL BE FILED WITH OR WILL BE FURNISHED TO THE SEC, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THESE DOCUMENTS, CAREFULLY AND IN THEIR ENTIRETY BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION AND RELATED MATTERS. Investors and security holders may obtain free copies of the Definitive Proxy Statement and other documents filed with or furnished to the SEC by STFC (when available) through the web site maintained by the SEC at www.sec.gov or by contacting STFC's investor relations department.

Participants in the Solicitation

STFC and its directors and executive officers and SAM may be deemed to be participants in the solicitation of proxies from STFC's shareholders in connection with the proposed transaction. Information regarding STFC's directors and executive officers, including a description of their direct interests, by security holdings or otherwise, is contained in STFC's Annual Report on Form 10-K for the year ended December 31, 2020 and the Definitive Proxy Statement. To the extent holdings of STFC securities by directors or executive officers of STFC have changed since the amounts contained in the Definitive Proxy Statement, such changes have been or will be reflected on Statements of Change in Ownership on Form 4 filed with the SEC. You may obtain free copies of these documents as described in the preceding paragraph filed with or furnished to the SEC because they will contain important information.