As stated, always trim after resizing.
And even if your neck sizing the brass, it can still stretch. This is even more so true if the brass has only been loaded once or twice, in which case I always trim once fired brass, and it has always needed to be trimmed.
I'll try not to go all long winded, been doing that a lot lately for some reason. But to get to the point, it is imperative to at least check brass length following each resizing session, whether your necking it, FL sizing, or other wise. In other words, never allow your brass to exceed SAAMI maximum specified length. If it exceeds max. there is a risk of the mouth getting pinched in the throat, which can result in extreme pressure spikes and can even damage the throat / chamber in extreme circumstances. OK, that's all.
GS