They were built between 1923 and 1924, 75 by Baldwin and by Lima Locomotive Works . The Class S-1a’s were built in 1926.
The text describes the production timeline for a specific type of locomotive (Class S-1a) by two manufacturers (Baldwin and Lima Locomotive Works).  It mentions that these locomotives were built between 1923 and 1924, with the Class S-1a model being introduced in 1926.