It depends. Usually little visual things like that I'll go back and fix, since my readers tend to notice those sorts of things -- so like, I have one character who lost a finger, and it was kind of a big deal when he lost it. I occasionally forget and draw him with all ten fingers, and if I notice this, I'll go back and fix it, because that's the sort of thing where if a reader noticed it they might wonder if he regrew the finger or faked losing it or something, and wonder if there were some magical shenanigans going on.
I have another character who wears a necklace. The necklace isn't important to the plot and has never been mentioned, it's just part of her outfit. If I forget to draw it in a panel or something.... I'd probably just leave that alone. Or I might eventually fix it for the book.
Generally, though, stuff like that isn't super important. It's amazing how you can establish that a character has a gun, forget to draw the gun for the next 20 pages, and then have them shoot the gun in a crucial moment, and most folks won't notice because you already established earlier that they had it. Some friends and I once cosplayed another friend's webcomic characters and SUDDENLY noticed hundreds of little things like this -- tiny outfit changes and inconsistencies and drifting/changing details from page to page, and the thing is, we literally never noticed any of these until we were sitting down to actually cosplay the characters. Prior to that? It had never mattered.
So it depends a little bit on how many clues you tend to hide in small details like that, but other than that, it's really up to you whether it's worth it to you to go back. Most of your readers won't really notice.