"Did ATSF ever have in their roster an E6 No. 12, or an F3 No. 22?
It makes absolutely no difference to me what the numbers are or whether they ever existed, but wouldn’t it be very easy to choose numbers that were indeed used by the railroad?"
All this info is easily searchable on the Internet. There is a Santa Fe Historical Society (and may others). There are rosters of locomotives for almost any RR you care to name - just search "roster ATSF locomotives", or variations on that theme.