Unpolished magnets where used in all the early P90s and PAFs-predominantly Alnico II, III,and IV-the move to using alnico V didn't come till about '61.
An unpolished magnet has a rough finish to it and is also longer at 63.5mm as opposed to the newer polished magnets at 60mm.
The magnets are made individually and cast in sand, the magnetic axis are then ground for a flush fit up to the pole shoe on one side and slugs on the other.
There are various claims of benefits of unpolished over polished/ground magnets but for me the slightly longer length imparts a more balanced response from the pickup. It's particularly noticeable in the unpolished Alnico Vs we use, probably because they're the most powerful, the tone isn't as hard/blunt as a polished magnet and string sustain is better too.
Also they're nicer to work with :)