I don't quite get what you are asking - I'm assuming you are questioning whether he has silent reflux, since the meds are not working.
When my child went on medication for reflex (around age 6) we were told to come back in about 6 weeks. We then kept records, and they felt that it could be a lactose intolerance as my other child has this. So we eliminated certain dietary items.
In the end, it turned out to be anxiety causing upset stomach and sometimes vomiting.
I kept records though and reviewed them with the doctor regularly. No sense in being on medication for 9 months if it is not working. I don't really get the point there. I'd ask for more tests or a referral to someone else. Who are you seeing for this?
I am very familiar with ENT as our kids have had tubes. Five sets of tubes by 7 years old? That seems excessive. One of my kids had their tubes fall out .. but five sets? We also had adenoids out.
Not sure how that (ENT) is related to reflux. Or why the ENT team would suggest it. My kid with the tubes and adenoids out did end up having allergies - and sometimes a specialist has seen cases before that seem similar. However, you should see the gastro team for the reflux. Not sure what they are called - for us, we just dealt with it as a trial and error thing and me keeping records.
Not sure if that helps - but I agree that sometimes allergies can be responsible for things like this. Our child's ear/sinus issues were all related to the excess fluid from his allergies.