Adult Co-Ed Rules/Blocks

[Fritz]

New to VB officiating this past year; done some youth league games and worked into a few HS subvarsity this past winter. Now into the Adult Co-Ed season and have a question for anyone else that does co-ed leagues.

The ones I have been doing all seem to allow one of the back row male players (if there are two at time of serve) to come forward and participate in blocks at the net. Yet their league rules generally say they are playing NFHS rules - if they even have a set of league rules. Thought back row players couldn't participate in a completed block.

Is this an exception generally granted to co-ed teams or am I missing something else?