That's interesting.
I kinda suspected something like that going on with the parts I buy. For example: I use a lot of Schaller Roller Bridges in my guitars, but occasionally I get one where the machining of the rollers and/or the threaded shafts is not done very well and the roller saddles don't move freely. Perhaps I got one or two outsourced bridges? The rest of them work perfectly smooth. I've occasionally seen the same thing with the tuners I use (Fender locking 18:1).