The company only made fans until 1922, when they started to sell radio components, then whole radio units around 1924, which lines up nicely with my math. The company was bought in 1929 by General Motors and thus was became the General Motors Radio Corp. I've never found a directory any later than 1929, but I suspect they were printed into 1930 since that's only 30 days after this issue. But later than that is unlikely as the company was liquidated in 1931 as a result of an antitrust suit.
This of course was back in an era when we actually prosecuted anti-trust cases. The General Motors Radio Corporation was owned 51% by GM the other 49% was owned by Westinghouse, RCA and GE. But why did they buy it? By 1929 the company was a total money loser, it was insolvent, and funded by Charles Kettering, a VP at GM. It's likely that they bought Day Fan just because they had an existing license from RCA for their radio patents. It further concentrated market share in the hands of a few. But it was very late in a game they were about to lose.
In 1930, the DOJ filed their antitrust suit against against RCA, General Electric and Westinghouse. They lost and the DOJ divided up the pie. GE and Westinghouse had to give up their shares of RCA. RCA stayed in the radio business and GE and Westinghouse had to get out of the pool. They couldn't even compete in that industry for almost 3 years. As a result the majority of the shares in Day Fan were owned by companies no longer allowed to sell radios or GM for whom it was ancillary to their core business. The General Motors Radio Corp. was liquidated in 1931. You can read more here here.
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