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@bmx1972 ...
These tandems were produced from early post war to 1963 and they had small changes in paint colors, components and markings that all help in actually dating them. Once the paint, decals, pins and parts are missing, it's very hard if not impossible to actually date them. The first ones had hand stamped serial numbers T001 to T999 and they were most likely used in a sequential build over the first few years of production. On Jan. 19, 1949 Schwinn pre-stamped some serial numbers on the BB shells starting with T001000 and these numbers were machine stamped. At this point these pre stamped shells were used randomly to build the Tandem frames. They were also used to build some early postwar lightweight bikes like the new Continentals. Your serial number has no recorded stamping date and since these shells were used randomly one can only guess the year the bike was actually built when it's in that condition with missing parts.
Here are the only recorded serials and the stamping dates.
01/19/1949------------------ T001000 ----- T001217 -(TDM)
07/18/1950 ------------------ T002347 ----- T002490 -(TDM)
07/19/1950 ------------------ T002491 ----- T002662 -(TDM)
07/24/1950 ------------------ T002663 ----- T003035 -(TDM)
Your serial number is T001628 so I would take a guess and say it was built in 1949-1950. The highest serial number I've seen on these was in the 5000's and it was a 1963 model. These stamping dates have nothing to do with an actual build date and the later stamped numbers were used all threw the 50's.