Easy, compare the chrome(US chrome is way nicer looking and Jap chrome looks cheap), the screws on the chrome, the screws on the pickups, the pickup covers, the decal, the pickguard, the threads on the bridge saddles, the bridge itself, the four switches are slightly taller on Jap jaguars, the knobs have no set screw(only visible in some online pics at the right angle), the trem arm and the trem arm collet hole, the tremarm collet, and the "fender" on the trem, serial number location, the dots on the side of the neck and you will notice minor differences in all these things. (I think I listed everything) They are only minor differences but they all add up to quite a bit of $$$$ if you want it to look 99% like (1% unless you change the decal,serial number decal,finish and side dots)and sound 100% an AVRI Jaguar. Hence why Jap jags are cheaper.
As a side note, the tuners that US and Jap jaguars/jazzmasters use are 100% identical, they are Gotoh "kluson" style vintage tuners. And Jap Jaguars have a thin poly finish(well mines very thin) and US jaguars have a thin poly finish with nitro over the top, both are alder. Older MIJ's are not alder.
