In short, all of the bipod sleeves should fit all of the gas cylinders - they're interchangeable.

As for the identification by mark/type, it's fairly easy as you've been told but the difficulty arises when parts are, say, interchangeable parts from, say, an Australianicon bipod are fitted to a UKicon bipod. That can cause a bit of head scratching. But if you do get confused and start to worry, I suggest that you load up 6 magazines, book the range and go out with another Bren fan on Monday lunchtime and let the first magazine go down in single shots, the next magazine in short bursts, as per the book, then the next 4 let them go hammer and tongs. You'll find that bipods dont have the same fret factor afterwards!