Hi Freddy,
I also noticed that the remaining file teeth 'pattern' is visible in the same areas on each knife. The blade is quite thick , so if a 'file' knife was undesirable they could easily remove the evidence (teeth pattern) by making the blade slightly thinner. Could it be like a 'quality' mark ....so that you could easily see what the blade was made from.
If that is the case I can only assume that 'file' knives were desirable by the locals.