Company: MYI
Filing Date: 2025-09-05
Form Type: 424B3
Source: 0001193125-25-196285
Chunk: 344

Company: BLACKROCK MUNIYIELD QUALITY FUND III, INC.
Filing Date: 2025-09-05
Form: 424B3
Chunk 344
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 deemed to be an underwriter;             |

| • |     | invest for the purpose of exercising control over any issuer, except that the Fund may control a portfolio 
 subsidiary;                                                                                                |

| • |     | purchase or sell real estate or interests therein other than municipal obligations secured by real estate or 
 interests therein;                                                                                           |

| • |     | purchase or sell commodities or commodity contracts except for purposes, and only to the extent, permitted by                          
 applicable law without the Fund becoming subject to registration with the Commodity Futures Trading Commission as a commodity pool; or |

| • |     | make any short sale of securities except in conformity with applicable laws, rules and regulations and unless,                                                                                                                            
 giving effect to such sale, the market value of all securities sold short does not exceed 25% of the value of the Fund’s total assets and the Fund’s aggregate short sales of a particular class of securities does not exceed 25% of the 
 then outstanding securities of that class.                                                                                                                                                                                                |

As a matter of fundamental policy, under normal market conditions, the Fund will invest at least 80% of its Managed Assets in investments the income from which is exempt from federal income tax. As a matter of non-fundamentalpolicy, under normal market conditions, the Fund will invest at least 80% of its Managed Assets in investment quality securities. For the purposes of the foregoing policy, an investment quality security is a security that is rated BBB or Baa or higher by Moody’s, S&P or Fitch or another nationally recognized rating agency or, if unrated, deemed to be of comparable quality by the Investment Advisor. The Fund has adopted a policy to provide shareholders of the Fund at least 60 days’ prior notice of any change in this non fundamental investment policy, if the change is not first approved by shareholders, which notice will comply with the 1940 Act, as amended, and the rules and regulations thereunder. The Fund’s VMTP Shares are assigned long-term ratings by Moody’s and Fitch. In order to maintain the required ratings, the Fund is required to comply with certain investment quality, diversification and other guidelines established by Moody’s and Fitch. Such guidelines may be more restrictive than the restrictions set forth above. The Fund does not anticipate that such guidelines would have a material adverse effect on its ability to achieve its investment objective. Moody’s and Fitch receive fees in connection with their ratings issuances. The Fund is also subject to certain covenants and requirements under the terms of the VMTP