Company: MYI
Filing Date: 2025-10-14
Form Type: DEFA14A
Source: 0001193125-25-238637
Chunk: 0

Company: BLACKROCK MUNIYIELD QUALITY FUND III, INC.
Filing Date: 2025-10-14
Form: DEFA14A
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A INFORMATION Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a Party other than the Registrant ☐

| Check the appropriate box:          |     |                                                                                   |
| ☐ Preliminary Proxy Statement       |     | ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |
| ☐ Definitive Proxy                  
 Statement                           |     |                                                                                   |
| ☒ Definitive Additional Materials   |     |                                                                                   |
| ☐ Soliciting Material Pursuant to § 
 240.14a-12                          |     |                                                                                   |

BLACKROCK MUNIYIELD QUALITY FUND III, INC. (Name of Registrant as Specified In Its Charter) (Name of Person(s) Filing Proxy Statement, if Other than the Registrant) Payment of Filing Fee (Check the appropriate box):

| ☒ | No fee required. |

| ☐ | Fee paid previously with preliminary materials. |

| ☐ | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 
 14a-6(i)(1) and 0-11.                                                          |

BLACKROCK MUNIVEST FUND II, INC. BLACKROCK MUNIYIELD MICHIGAN QUALITY FUND, INC. BLACKROCK MUNIVEST FUND, INC. BLACKROCK MUNIYIELD QUALITY FUND III, INC. Important Information Regarding the Proxy Statement, dated September 8, 2025 for BlackRock MuniVest Fund II, Inc. (“MVT”), BlackRock MuniYield Michigan Quality Fund, Inc. (“MIY”), BlackRock MuniVest Fund, Inc. (“MVF”) and BlackRock MuniYield Quality Fund III, Inc. (“MYI” or the “Acquiring Fund”) The Section of the Proxy Statement entitled “Voting Information and Requirements – Voting Requirement for Proposal 2: The Issuance of Acquiring Fund Common Shares” is revised and restated to provide the following information: Voting Requirement for Proposal 2: The Issuance of Acquiring Fund Common Shares

| Proposals                                                                                                                                                          |     |