I'm certain Yates was hitting slin as well mate. Fact is once GH is used at a high enough dose for a long enough period the user is then forced to use slin no matter what because the GH drops blood sugar way too low. So slin becomes a part of their everyday routine, though being BBers they take advantage of this and use higher than needed slin doses. It is the slin + AAS that really gives that freaky bulky round look to their muscles, whilst the HGH facilitates this and aids in new fibre and joint growth, fat loss and also directs the nutrients into the muscles rather than being stored as fat. This is why they always recommend using GH when using Slin as it decreases the chance that the Slin makes the user gain fat, the AAS also decrease this as well. They all work synergistically with each other.
Looking at ronnie, i'd say he exploited everything. There's been speculation as to what these guys use in the on and off season, though their off season cycle alone is absolutely insane. I won't post any details up here because i don't have 100% proof, all we have is speculation and rumours etc. A lot of these speculations come from pro's themselves and advanced trainers.