When I was in ASL classes many moons ago, my instructor was from a family in which he and his two sisters were Deaf. The instructor was known within the Deaf Community to be extremely skilled with ASL, that is, he was very skilled in story-telling.
So guess what happens when his sisters come and visit the classes. They had good natured arguments over various signs and whether they were ASL, PSE, SEE, or what. Here's an example of what happened.
During class we had a vocubulary building exercise in which everyone was to show a style with a particular hand shape and then fingerspell the meaning of the sign. On this evening, the handshape was the letter S. So his sister made two 2-handshapes and pulled one hand forward and one hand backward. She then fingerspelled S O. Her brother looked at her and was like "what the heck was that that?" She again fingerspelled S O, and he replied it looked more like "rip" or "tear" and it would be much faster just to fingerspell it. The entire class simply broke up with laughter. We all knew they weren't having any sort of serious disagreement. It was fun seeing sibling teasing in ASL.
The moral of the story..... Just be flexible. Just because someone uses a certain sign, it doesn't mean everyone will know what that sign means. Ask the person what the sign means and continue.