Just be careful with the books too. It is my understanding that this is where the Proofhouse data mostly originated. They just aggregated various sources.

A particularly notorious example for Colt is R.L. Wilson, of course. And I’m not talking about his criminally fraudulent activities, but data in his books which Colt collectors have relied on for decades, but at least some of which we now know to be simply fabricated.

In an era of my interest, WW II revolvers, Proofhouse (and the Colt online serial look-up too) use fictional date ranges on the Colt Official Police going back to Wilson’s “research”, providing serial ranges for 1943 to 1945, when no OP’s were produced. I’m not in a position to generalize, but would use no Wilson data unless backed up by a sufficient primary database of archive letters.