So glad that F's is doing better, Martina!
It's possible that he's fine with hidden dairy and things like cheese and yogourt. There are degrees of MPI - some babies can't tolerate ANY dairy at all (even hidden/trace), some are fine with hidden, some are fine with everything but can't tolerate straight milk. And I have heard too that MPI can be outgrown at any age (though certainly more common as los get older).
You really have a couple of options if you're not sure. You could continue to introduce things gradually and make note of any changes in his behaviour/symptoms. That might be a challenge though, since you might not know if symptoms are the result of the dairy, or of OT, OS, reflux flare, etc. If you're feeling brave there is another option... When I did dairy elimination for Dylan's eczema I avoided everything, including hidden/trace, for 1 month. I didn't really notice any improvement, so my doctor suggested that I reintroduce it in a BIG WAY - that way, if his eczema flared up I would know what the problem was. Sometimes things get better so gradually that you don't notice that the are improving, but when you reintroduce the offending food a flare up of the symptoms happens quickly. It sucks, but then you know. I don't know if the same thing would be recommended if Dylan's symptoms were more serious than *just* eczema (like blood in the stool for example), but that's what I did. I had a grilled cheese sandwich, a big glass of milk, and about a dozen chocolate chip cookies
His eczema did flare up some, so I knew that my elimination was actually helping.
Don't know if that rambling was helpful at all