Welcome to the forum, RetroGrade. I'm not sure if Europe had the same problem with overlapping generations but yes, here in North America it's often best to say your 1987 al25 is one of the earlier production years so that you don't accidentally end up with parts for a 3rd gen car. The 87 I just bought actually came with some spare parts but surprise surprise, some of those spare parts were for a 3rd gen! They had been bought online and there was no way to return them so I gave them away locally.
To answer your other question, almost all the parts in the 4wd wagons are interchangeable regardless of year. The transmission/diff ratios changed between 84 and 85, same with the grill and headlights, but again that's here in North America so it might be different in Sweden.
In case you're interested, here's a fairly complete list of changes to North American al25's over the years:
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