Hello Michel,
Jacques and Bill could probably answer your question better than I am able to, but as far as I know the hole pierced through the back of the camera had already dissapeared before serial number 12,000 was reached.
The hole in the pressure plate continued until much, much later. We can only assume that either the pressure plates were produced in vast quantities during 1934, and 1935, or that the Fed factory didn't see the need to modify the punch that stamped the plates out. After all the hole does no harm, and isn't detrimental to the operation of the camera.
That said I have several Fed 1a and 1b prior to serial number 12,000 that have the usual pressure plate with the hole, but no hole pierced all the way through the back.
Your camera serial# 28581 is as I would expect, ie hole in the pressure plate but not pierced through the back.
So we come full circle and that is to say that there are no hard and fast rules where these fascinating cameras are concerned, but that's just part of what makes them so special.
Cheers, Jim


