I agree fixit...
I've never had an inspector fail a sprinkler system... and in most cases they've left it completely alone.. in about probably 40-60% of the cases the homeowner is simply trying to do the 'right' thing...but don't over do it.
Other times it's left in dis-array...
Interestingly enough though stats state a sprinkler system can add 1-3% of value to the property up here.
So a check valve down stream of a stink ugly avb valve above ground ... far from the list of priority...
Again if it happens.. Big whoop just fix it