They have changed the actual core RIP engine several times over the years in different major versions. I know they used to use APPE (Adobe PDF Print Engine), then I think Aurelon, and I think now Mako (Global Graphics). I think that is why between various versions that use different actual core RIP engines that color profiles and whatnot get all screwy and dithers change. Like all of our old profiles used So Diffusion dithering which worked awesome for really smooth solid colors (particularly in lighter shades) and is what we built all of our own custom profiles on. Then in the newer version that dither is not supported (even though I personally think its superior) so the new version offers to convert your profiles. Then everything prints grainy looking. I tried and tried making all new profiles using various other dither methods in v21 and none looked as good as our old profiles. Got tired of fighting it and went back to v12 for now as we just need to get work done for existing clients where we need to match what we did a couple of years ago.
Eventually when I have some extra time and tons of vinyl to waste I'll probably try again.