Interesting topic, this. Looking a bit wider, it was the case that in Russian, French and Italian aviation manufacture no such masks or templates were used. I could not state this was so to 100% certainty for Japanese aviation, but I think it was quite likely true there, also.

The application of camouflage in this way was seen not only to be practical, but also desirable. Such a strictly repeating pattern, surely, would draw the human eye just as readily as incongruous colouration. Random deviation from the agreed pattern idea was regarded as a counter to this problem, and was widely encouraged in those countries’ manufacturing programmes.

However, military thinking being what it is, strict conformity was required by some Air Forces. This was self-evidently the case with the RAF, and it seems that some US manufacturers did likewise. Certainly we can say that Curtiss employed such mats (at least sometimes) for factory applied camouflage, as this image shows these being used on some P-40 aircraft. Whether these are similar to any mats used similarly in British manufacture, I cannot say.