It's actually early-mid July when the special builds that aren't getting updates started hitting, so a June car would probably have been on 2021.4.x and we have several cases of those getting main branch updates. The more I learn about the versions cars ship with from the factory and the verison they update to, the more I worry that it isn't just two groups of IC shortage cars (2021.3.x and 2021.11.x), but actually several. It seems that 2021.3.x builds actually were on most cars for a while and they would just get normal updates right after delivery (usually the same or next day) to one of the 2021.4.x versions. It isn't until the 2021.3.104 build that cars stopped getting updates. Note that a great many 2021.4.x cars also stopped getting updates after their first few and have been stuck in that branch for several weeks too.
The fact that the lower build numbers aren't even being updated to higher build numbers in the same branch makes it seem like they may all be incompatible with each other. For instance 2021.3.104 has been out for almost 10 weeks, but 2021.3.105, .106, .106.5, and .107 all have come out since then and none of those .104 cars has moved to any of the newer 2021.3.x builts.