To me: Fresh Orval has that crispness to it that I associate with Brett in clean beers, an almost dry, brut-type of finish. I may be associating something else that is making that and falsely equating it, but it is unique to Orval, for me. Older Orval just gets more dry to me. Like all clean Brett beers do in my opinion. There isn't anything funking it up, it's just Brett, and a clean fermenting sacch. Though the Brett could play with the phenols from the sacch that was used to produce some funk - the lack of phenols prevent this, in my opinion. Mostly, in Orval - to me, it translates to dry and less hops the longer it sits. The sacch they use is very clean I believe, which limits the phenolic production and thus the interaction between them and the Brett.
I have some 20 year old Orval that tastes pretty close to 1 year old, just super-dry, no hops, and no funk. When I'd drive to Orval and pick up my share, and the Petit available only there, it would be similar, just a bit hoppier, slightly sweeter, and no funk. I'd have more, but America thinks the beer should cost 6 bucks a bottle! When I was buying it at soda prices it was more doable.
I wish I would get this funk people keep referencing in Orval, but I have yet to find it. Tart, dry, crisp - yes. Maybe I just don't notice it? But I really love sour and funky beers, brew them all the time, and drink and visit as many producers of it as I can. I seek them out to judge in comps, so I think I know them well enough.
I've also heard that Orval purposely puts a different strain in at bottling to thwart would be yeast ranching...but that is based on hearsay and conjecture. I cannot confirm this. It is just from the rumors people keep stirring. And a different strain of Brett at that!
MTF has a very in depth analysis on Orval...but Orval is a super-clean beer before any Brett, as I understand it.
But I'm no biologist, so I could be just imagining what I think.