Modern Perforation Variations

What I like most about this stamp community is that there are so many experts in so many fields.
Here is the Folklore issue of 1990 with the rarer perforation 12.5 x 12.0:



I can visualize how many stamp varieties originate (colour, shifts, scratches, paper) but I can't think of how a change in perforation would occur.
Does somebody rush in, mid-production, and say "Stop the presses! We're using the wrong perforation"?
or "This 13.3 perforator is getting dull, but all we've got is this old 12.0 one"?

I'm sure there are some of you out there who know the answer to this question that has bugged me for quite a while.

Thanks for posting this sak. I also have this pair on a complete card from the Legendary Creatures English folder.

Both stamps have the rarer perforation 12.5 x 12.0, which are valued as mint $15.00 each and used $5.00 each on page 273 of the 2018 Unitrade.

So why is it listed under the Stamp Sponsorship Program heading on page 642 as valued at only $7.50 (complete folder with the postmarked pair).

I'll copy my comment to Mr. Robin Harris.

sak It can be for any of the following reasons:

1) Different perforators for different printers or change of printers
2) Different perforators for different stamp formats such as sheets, booklets, coils, etc.
3) Different perforators available at the printer that can be used there
4) Different perforating plates to replace broken or worn down plates

Since the 12.5 x 12.0 gauge perforating plate was used before and
after by Ashton Potter to perforate other stamps, it was also used
to perforate some stamps from this issue too.

see http://www.bnaps.org/hhl/TopicsDisp...p?issue=1842