Great summary, Ratnik!
Just my 2 cents - I think what you called "top barrel band" is normally called "top handguard" in English (equivalent of Ukrainian "цівка"). "Barrel bands" are pictured along with swivels in your summary and are equal to Ukrainian "кільця цівки". So what you called "swivels" technically are swivels plus barrel bands. That's how I understand English terminology, which is sometimes very different from what we've got used to, but I'll let native speakers correct me if I'm wrong.
Now, here's my question: do you find that all early handguards have flat top and all late handguards have raised profile with one step? Or the flat/stepped profile feature is not related to the 7 or 8 holes version?