I think the problem is that the subcompact kits WILL work on either a Gen3 or Gen4 frame, but all the other kits (for the larger guns) WILL NOT. From the Advantage Arms FAQ page:
Q: Will any conversion kit fit the new Gen4 Glocks?
A: No. You must use a kit that is marked for use on the Gen4 frame. For example, 17/22 Gen4, (see picture). Kits are currently available for the G17/22 Gen4, G19/23 Gen4 and 20/21 Gen4. DO NOT use any other Advantage Arms Conversion Kit on your Gen4 frame. SEE NEXT Q&A FOR INFORMATION ABOUT G26/27 AND G29/30 GEN 4 GUNS
Q: When will you have a kit available for the G26/G27 and G29/G30 Gen4 guns?
A: No special kit required for the G26/G27 or G29/G30 Gen4 guns. Our L.E. 26/27 conversion kit will work on all G26 and G27 frames, including the Gen4. Our LE 29/30 conversion kit will work on all G29 and G30 frames, including the Gen4.
I'm guessing the reason for this is the new Gen4 dual-spring Recoil Spring Assembly. It is larger in diameter than the old RSA, so the barrel, slide, and frame in the larger Gen4 guns had to be modified to make room for it. The Gen3 G26/G27 size guns already had a dual-spring RSA, so there were no changes to the barrel/slide/frame needed to accommodate a larger RSA; so, the kits will work with either Gen3 or Gen4 subcompacts.
Hope this was helpful.