Glenn,
Use of this filter agitators appears to have started with the 1985 XP models. WP's (and Kenmore's too) variations can be mind boggling.
The LA5000XP went from revision 0 to 5. There were a lot of DD revisions in the first few years, as compared to BDs of the same period. The 0 and 1 had the one piece agitator, part number 63235, while versions 2, 3, 4, and 5 had the removeable filter version. Must be a machine enhancement they made during the run.
The LA7000's drawing is deceiving, because it looks like a filter agitator, but it isn't. This is actually almost the same agitator, but the center section is not a filter, that's why there is an under basket disk filter included. That agitator kit is part number 64214, and the part that is the filter in the other agitator is called an "extension" on this one. Don't hold me to this, but I don't think the extension was as easy to snap off the agitator base as the filter is. One of my co-workers had his filter section come off the agitator during spin...can you imagine the noise?
I think several of the '87 models (the XS) changed to DA style agitators as soon as WP was able to start using them. They must have been somewhat anxious to do so to change their models mid-stream, vs. waiting for the XT versions to debut.
Gordon