7. There Used To Be an 8 train

BMT map from 1924
Map in the public domain. Source: Wikipedia user GifTagger

IRT train service connecting Grand Central directly to Astoria existed in the early 20th century. The IRT and BRT/BMT shared service along the Astoria Line from Queensboro Plaza (as well as along the Corona Line, now the Flushing Line). Queensboro Plaza was twice as large as the current station partly because the IRT also arrived into Queens from the IRT 2nd Avenue elevated line over the Queensboro Bridge.

The BMT 8 train (not the IRT 8 train, which was a completely different later service) was a BMT service from Queensboro Plaza to Astoria, and later once the BMT 60th Street Tunnel was built, it was also a service from the Broadway Line to Queensboro Plaza, where BMT subway customers could transfer to a BMT shuttle elevated train to Astoria. Because both the Astoria and Corona lines were built to IRT specifications, and IRT trains are narrower than BMT subway trains, BMT trains from the Broadway Line could not continue to Astoria until those platforms were physically shaved back and the Astoria Line became a BMT-only operation.