As Peter mentioned, the country and year is on the stamp. I am unsure that you find the stamp with overprint in general catalogs, I believe Mexican stamps of this era were overprinted with specific Postal Districts. MEPSI
http://www.mepsi.org/ is a good resource but the website itself is old and out of date. (I have contributed a new site to them, but it is not yet 'turned on' as their new web design guy is still coming up to speed.
Don