hi there
this sounds downright odd to me. the fluctuating pressure you found, i mean. i should be interested to find out why. could it be a variable heat source near the gas pipe causing expansion/contraction? just shooting in the dark really.
as far as the retest goes, surely they can only test for what is actually present. otherwise there would be a whole rake of 'fail' items, because you 'could' add them later. after all, you 'could' fill your bilge with petrol, in old oil cans to boot, but... i mean...
well, face/palm
sorry i can't be more helpful
best of luck
nigel