Some delving into it with internet searching (which may or may not be apocryphal), it seems that it was standardized/published by the Cycle Engineers Institute (CEI) in Britain first in 1901 and in 1938 were revised as BSC (British Standards Institution as BS811:1950 and thereafter known as British Standard Cycle). By 1950 the standard of having 20 threads per inch with a 60º cut had been dropped but was still included in the index. 20 tpi is more common in Whitworth threads (BSW) but those are cut at 55º. I read that some early Campagnolo cranks were cut to 55º 9/16-20 threads and were considered an Italian thread.