Here are my 3 mags:
Stamped blue with aluminum bottom SN# 1862 i, Side marked 122 with Eagle 37. Came with my 1936 Mauser.
Nickle/wood bottom, SN# 5888 b with a "+" mark below the SN. Came with my 1915 DWM.
Nickle/wood bottom, SN# 4331 (no suffix letter). Purchased separately