Was anyone able to find information regarding the different perforations? I tried and failed. I did look at a Bulgarian dealer's (located in Bulgaria) material and every stamp but one had the smaller perforations. I find it odd that it is not talked about when other less obvious differences between stamps are picked apart in great detail.
No, I've not seen any references to this.
I guess catalogues won't usually list different perforations unless the gauge is different.
Even New Zealand's distinctive Chambon perforations aren't listed in most catalogues.