Not sure this is entirely true, my Jag is an '08 and the neck is stamped MIJ.
I could be wrong. I have been in the past. I lurk on a telecaster forum, and that is where I read about it. I may have misunderstood or it only applies to teles.
Regarding hum...
Mine has a slight hum that comes from single coils, but nothing major. The shielding job I did helped... but it wasn't really objectionable in the first place. Keep in mind, mine is modded so that I have have independent volume controls for each pup, so I will get single coil hum when the volumes do not "match".