More likely they're rerolling or relabeling cassettes intended for disposable cameras in the first place -- 27 is a very common frame count for those, and never mind if that count only applies if you can load the camera in the dark (hence avoid fogging the leader and first couple frames). I can usually get 27 frames on a properly marked 24 exposure roll with my Rollei 35, but that isn't going to happen with a full size 35mm SLR or my Kiev 4. One, maybe two extra frames (or one and a half, more commonly) is about the limit.