The glass plate sizes were relatively well standardised, eg whole plate, half plate quarter plate, although other countries had metric and imperial versions. Before the plates were mass produced they may have varied more.

My dad collected old cameras, he had 100's, and the number of formats in use was not all that much smaller than the number of cameras, to the point that we had to cut glass or paper quite often. We also sensitized our own plates and developed metal plates (which is insanely dangerous).