Was The Dick Van Dyke Show the first show ever to announce its conclusion at the end of a U.S. Broadcast TV season in advance?

I don't know at this point if Leave It to Beaver did the same, considering that LItB had the first official series finale episode on U.S. Broadcast television. I couldn't find anything regarding Leave it to Beaver's end in the Broadcasting archives.

Source: Broadcasting Magazine (January 3, 1966 issue, page 128; Article: "Van Dyke Cuts Self Off") (https://worldradiohistory.com/hd2/IDX-Business/Magazines/Archive-BC-IDX/66-OCR/1966-01-03-BC-OCR-Page-0128.pdf).

Let me throw out three shows that may fit this category, I Love Lucy, it was the number one show when it went off the air, and I believe it was public knowledge that show was ending prior to the season finale (of course the format was somewhat revised into a number of hour long specials that appeared over the 57-58, 58-59, and 59-60 television seasons but it was under a different title). The Danny Thomas Show was still in the top 10 when Danny decided to end the series (again I think it was public knowledge that the show was ending). Burns and Allen ended because Gracie was retiring, I believe that was public knowledge.

Although this doesn't answer the question, Leave It To Beaver and DVD both ended with clip shows. DVD produced another episode after the clip show, which was shown for years after the clip show, in syndication.

The DVD clip episode felt more like a final episode than the LITB one, mostly due to its tag scene, which definitely was intended as a wrap.