The TT database, like the old Shell-BP History of the TT (& the Manx!) lists only those riders who actually started in a race.

Those who entered but non-started, even though they may have practised, do not feature.

Howvever, if we assume that Stanley was born in 1907, then we may look in the entry lists from, say, 1927 to 1939.

Sorry, I can't find him in any of these as published in the magazines of the time, so it looks as if he wasn't a TT rider.