Tony,
you can not always tell from a loose stamp (or even strip or block) the base!
As the stamp size has (normally) 17 teeth / 25 teeth I used to denote the perforations as:
17/25, 17/25- or 17/25+ (for the base 17) or 25/17, 25/17- and 25/17+ (for the base 25)
It is a phenomenon I met - for other countries but including Argentina! - some 40 years ago .... when I was comparing the perforations of the Dutch stamp printers and grouping them into "families" - some of these Dutch families are quite large.
There is a B14 for Switzerland, a B15 and a B18 for Luxemburg; the J1 is an enormous family just like the J2.
The Dutch printers have a good documentation of these perforation blocks they had made themselves upto now! I met the guy who is still responsible for the blocks and cylinders and he is constantly working with needles and pins!
see :
http://galeoptix.nl/fila/jezabroa.htm
to be continued ....