Intentionally shortening cases was common when the M14 was still the primary service rifle for match shooting. The hard extraction with a full power load caused everyone to favor military brass for its greater head and rim toughness, but it was common for that brass to have detectable internal pressure ring thinning after about the fourth reloading (fifth firing, counting the original factory load, if there was one), so it had to be tossed. Since it could grow as much as about 0.010" per load cycle, a lot of fellows started trimming 0.020" to 040" below minimum spec when they first got the brass, just so they'd never have to trim it again before they retired it. I've never heard of this causing and issue. Their bullets would mostly have been the 168 grain Sierra MatchKings, so they had a little more bearing surface than a 150 grain BT has to hang onto. They shot fine.
Consider that most chambers have throats about 0.005" to 0.020" longer than a maximum length case to begin with, and you can see that extra room, by itself, is not an issue. What will be a potential issue is the shorter necks may simply not hold onto the bullet well enough to get best start pressure. You would learn about that with a chronograph by looking for increased velocity standard deviation. Otherwise, though, if the bullets don't fall out, you are probably good to go ahead and use them until they grow back.