On the sample two I can provide, both bikes had the numbers stamped onto the underside of the BB.
The 1982 Mercian Colorado is stamped 45882, with an 8 stamped under that. According to Jane at Mercian, it's the 458th frame of 1982, by builder no. 8, George Bryan. The numbers are between the under-BB cable tunnels.
My KOF 2002 Vincitore is marked with a 5 right at the juncture of BB shell proper and the DT lower lug; 191; below that, 2002. Builder no. 5 (Derek Land), no. 191, and built in 2002.
The c.1969 Mercian Olympic that belongs to a friend of mine is not readily accessible, but it, too, had similar markings under the BB shell.
Russ Fitzgerald Greenwood, SC
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