That would be my guess, especially if just some pressure from a pencil moved it back.
As for trimming handgun brass, some people don't, some do. But at least segregate it by maker and check case OAL. An extreme example is to compare say Winchester brass against S&B, S&B cases in 9mm are notorious for being at or below the SAAMI minimum length, Winchesters tend to be around the midway point. If you set your crimping die for the Winchesters and then go to crimp the S&B it won't even touch it.
Reloading is a series of variables, to get the optimum loads you need to reduce those variables as much as is humanly possible. The thing about trimming handgun brass, which admittedly doesn't stretch as much as rifle brass (but it does stretch, it has to) is that you only need to do it one time over the expected life of the case, if you'r lucky enough to get 8 or so loadings out of it I'd check em and retrim but to me they'd be suspect for mouth hardening anyway, splits will start to show up.
When I buy new pistol brass, or the first time I use once fired, I take the time to trim them, it's slow and onerous, but IMHO should be done.
After that first time, I don't sweat it, just check them every few loadings. How else is one supposed to get a uniform crimp if every other case isn't uniform in length? If you want to just reload to make noise then don't worry about it but one of the benefits of handloading is to strive to make quality ammunition, not just smoke.
RD
