I'd say the pickups with stamped serial numbers are made by Maxon even if they also have a sticker like a Dry 82 or Screamin sticker. There are a few of these stamped serial number and sticker pickups mainly from around 1982 which seems to be at the same time as the Maxon to Fujigen pickup making transition. In other words the pickups with a stamped serial number and a sticker could be called transitional pickups and are probably made by Maxon. The Fujigen made pickups don't seem to have a stamped serial number and only seem to have a sticker but there might be exceptions. The pickups with only a stamped serial number before 1982 are made by Maxon as were all the early Ibanez pickups as well.
Fujigen probably had a fair few Maxon made pickups stored away in 1982 and they probably just put their pickup sticker on them.
When things change at any factory there are left over parts from the previous things and so on, so some things are produced after the change with things from before the change.
The same thing happens for saxophones for instance where some new models are made with parts from the old model. This happened a lot. Like a very early Selmer Mark VII model sax might have a previous model Selmer Mark VI body and parts but be stamped as a Mark VII model.
Same thing happens when the Grecos change from the Super Reals to the Mint Collection.
The pickup above has a 820407 serial number and a Screamin 1982 sticker
Maxon date code = 7th April 1982 so it makes sense
Another 1982 Greco pickup
820225
25th Feb 1982
I don't know about these Greco pickups
First number = Nisshin Onpa (Maxon) pickup code (1, 2, etc)
Second number = Year (9=1979)
Third and Fourth number = Month (01=Jan ... 12=Dec)
Fifth and sixth number = Day of Month (01-31)
