The biggest difference is the 1900 lacks the Purdy style forend release. The 1900 used a snap on forend similiar to a Parker Trojan.

The 1900 came in only 12 and 16 gauge ('94's came in 10ga) and there were no graded 1900's. Checkering lines per inch was more course than an A grade 1894, 18 lpi vs 20 lpi. Barrel fit to breach balls of reciever was less precise. 1900 serial numbers were in the 300,000 range.