This was a long time ago, but on this picture there is indeed more than one chamber, judging by the darkened areas. The buds were also very 'loose' as can be seen on the previous picture, thus it all seems to point to the midge (Rhopalomyia solidaginis) rather than the fruit fly (Procecidochares atra). The interesting thing was finding that parasitoid, I think.

Okay. I'm truly seeing only a single, hollow chamber per gall. It looks like two per gall here because they've been sectioned vertically. These are not loose in the sense that Rhopalomyia solidaginis galls are, where the leaves surrounding each of several chambers per gall are long and skinny and distinct. R. solidaginis chambers are not darkened, and are instead translucent and held above the stem of the plant, roughly where a bud would be. Also, I think it's basically unheard of to find so many distinct Rhopalomyia solidaginis galls on one plant. There's usually just one cluster of leaves at the terminal bud of the plant, though that cluster may contain several chambers.

Yes, you are absolutely right. Sorry for being so obtuse. It was indeed a long time ago and I have been refreshing my memory. Indeed in the past I have found a true bunch gall at the top of the stem, see below. I hope that you would be able to move these to the right place.