Probably best to do it from both way, back track from G005.1, and forward from the X input, IF you know the assignment.
There is a common method used to operate the FIN signal and usually it ends up with a small rung with R- registers used by the various FIN signals from different M code sources or completions.
One advantage with the original ladder hard copy, it usually has all the bit assignment labels printed in, and also all the rung numbers where a bit is used, this helps tremendously when trying to decipher a unknown ladder.
Al.