The 'Society of Model and Experimental Engineers' I believe hold the Drummond archive in their library. Twenty odd years ago I was their chairman, but having moved away I'm no longer even a member !
B-Type Serial numbers:
1912 - ( ? )
1913 - 1914 Serials 700 to 1516
1914 - 1916 Serials 1517 to 1731
1916 - 1918 Serials 1732 to 2003
1917 - 1918 Serials 2003 to 2173 (separate pages in ledger)
1918 - 1920 Serials 2173 to 2338
1919 Serials 2339** to 3002 (separate pages in ledger)
1919 - 1920 Serials 3003 to 3464
Serials 3465 to 4058 (separate pages in ledger)
1920 Serials 4059 to 4190 (separate pages in ledger)
Serials 4191 to 4224 (separate pages in ledger)
**Lathes up to No. 2339 had two machines against each Serial Number i.e. two different customers, dates and production ticket numbers for each Allowing for numbers duplicated, total production of the B-Type would have been around 4000 units.