is there a way for me to determine if it is 12 perf or possibly 6? I am thinking it is probably 12 all around - but wanted to ask for advice.
The trick is, to set aside a known stamp of guage 12.
(It can be any country, pref. a duplicate, write on back "PERF 12")
Then simply take your unknown Mexican, place it alongside your known perf, (both face down) and I bet you will see the perf tips (Teeth) line up or not.
Does not matter if there are huge gaps, the teeth will look aligned if the guage is identical.
Keep the Perf 12 guaged stamp, in a glassine front of Album, for later use.
Similar method how I measure my Turkey Guage 7 (Largest on my Perf Guage)