Supposedly there are all kinds of differences.
But the caveat about that is that, the people who like Jackson pickups aren't necessarily sane, so you have to take their anecdotes with a grain of salt.
I've seen a few raging debates about how to tell if a Jackson pickup is MIA or MIJ. If there were even MIJ ones in an era, etc. etc. etc.
Which is a big question, because that effects the value of the pickups. MIJ is only worth $4, MIA is worth at least $7.50.
I've sold a couple Jackson pickups, the ones that were desirable enough to sell, the others get thrown away. JE units too.
People who buy Jackson pickups absolutely do care if it came from an MIA guitar. There have been a couple MIA ones I bought where I just pulled the entire harness with the pickups and the shielding plate and people were going nuts over it.
Although if you are selling Jackson parts from that era there is a 50% chance it is going to be to AlienXNation, so he can relist them for something criminal on ebay. The other 50% will be some dude in a country you have never heard of who will ask you if you are selling anymore and then they will say something like, "PUT THEM ALL IN A BOX AND SEND THEM TO ME".
AlienXNation is weird, because half the time he buys your shit to flip he'll buy it under the AlienXNation name, and the other half he'll have an unconvincing alias account.
I have no problem selling it to AlienXNation, if he is crazy enough to sit on a $2.50 pickup for years listed at $130, good for him, but it's really fucking bizarre when it's one of the alternate accounts or another less prolific Jackson reseller and they pull the old,
"I am a blind Grandmother on disability who has always yearned for a Jackson pickup in memory of my dead son. Here is a message that totally doesn't make it obvious I think I have just suckered the deal of the century out of you, you ignorant fool. You don't know what treasure you have."
At least 40% of Jackson pickup sales will be to someone who totally thinks you don't know what you have. It's hilarious.