This is from a post by Doug Elliott (no relationship to me) on another forum. He is long time Ideal/Lyman collector/historian, many here may know of him.
Since there are many inquiry's regarding how to ID certain things about the moulds, I thought this might make a good Sticky.
Frank
As was explained to me some years back by Lyman's Tom Griffin, this is a quality control code for the cherries made for them by various outside suppliers. "BW" indicates the second (B) #457193 cherry made for them by supplier "W"; and "BV" the second from supplier "V".
Another letter/number code sometimes found might be something such as "F1", indicating that the mould was cut by employee "F", on machine "1".
The one-, two- or three-digit number on each pair of blocks is a "match number" assuring that the pair is kept together throughout the machining, finishing, assembly and packaging process.
A tiny pair of additional match numbers sometimes is also found on the collar of a hollow-point or -base plug and one of the blocks it is fitted to.
Other tidbits: Vent grooves were added to the mould blocks sometime in the early-to-mid-1950s; the company's stamp was changed from "IDEAL" to "LYMAN" in 1964; and the company move from Middlefield to Middletown in the summer of 1994 is also reflected in the address stamping.