I shouldn’t answer on the grounds that it may incriminate me...
DECADES ago when I started, before UL came up with the “classified” breaker program, Siemens/ ITE/ Murray, Bryant/Westinghouse, Sylvania and Crouse Hinds brand breakers were all designed on purpose to fit in each other’s panels. The term we used back then was “Universal” breakers (or words to that effect that varied regionally). They were never UL listed as such, but nobody cared, including AHJs. So at the hardware store they would have a section with Square D QO breakers, one with GE, one with FPE, one with Zinsco, and one section with Universal breakers that could be ITE one day, Bryant the next, Crouse Hinds next week etc. There would be just one bin with whatever brand was shipped to them all mixed together.
During that time a lot of people, me included, looked at the GE breakers and noticed that you could easily “modify” them to match the “Universal” format. It was never right, even back then, but in a pinch, you did what was necessary.
UL along with the inspector associations put a stop to that entire universal concept, I think in the late 80s /early 90s, by pointing out that if panels and breakers were not tested and listed together, they were a 110.3 violation.
Square D HomeLine came out just as all of this was changing so even though they were made to let SqD take advantage of the universal concept, they were too late. But that has not stopped people from plugging them into other brands of panels once they found out that they fit. Old habits die hard.