FYI, dimer and other impurities do not cause GH "on target" side effects involving water retention, like carpal. Those are normal and expected from GH depending on dose and individual sensitivity. It's GH doing what it does.
If the same dose (by volume) with one brand produces standard GH sides, and another doesn't, either the one with more sides is overdosed, the one that doesn't underdosed, or there's a difference in potency / biological activity (functional GH ie, it attaches to receptor or doesn't).
Contaminants may cause site reactions, immune responses, but not the exact same effects you'd get from GH that's working properly.
So TLDR, more GH specific side effects means you have more of or more potent GH than the one that doesn't.