OMC(Johnson/Evinrude)used the following for many years;
INTRODUCES
1234567890.
The last two letters is the year of manufacture.Maybe BMC uses the same?
Mercury/Mariner did have the date on serial#tag on later models.You can go to their website and type in serial#(Parts Express).
Yamaha is the last letter in model designation.Start with “C”(2004)and read reverse.
If the serial tag is missing,the serial# will be stamped on the powerhead.If that is altered/missing,motor is probably stolen.Friend of mine got one like that on ebay a few years back.I went to replace waterpump and could not find a serial#.Did a guesstimate on year,and it did work.
Hope that helps.