Different versions of the same lock?
I don't know, but wouldn't a different version require a new name, or a new part of the name or something. I think that would be fair.
Do the 10 and 13 reflect the thickness of the shackle?
The 10 and 13 do not reflect the thickness of the shackle. 10 and 13 are simply security ratings on Abus internal security scale. As far as I can tell they are visually identical and if I unlock them the steel shackle inside the lock is also 13 mm wide in both of them. If there was a security upgrade in one of them it must be something a buyer cannot see. That's what bothers me, I can't find any information about the difference.
Have they been tested in the same countries?
Well, I'm from Europe so I doubt Abus tests their locks anywhere outside Germany.
I believe they have both been tested in Germany its just that 10/15 version is probably the older version. It has NEW written on a cover.
Both have the same "outside" security ratings like Sold secure, Art, etc. But those ratings only use three or five star system so the ratings for both locks end up being the same. The Abus internal security ratings do show a difference and I wonder why.
Abus site suggests a 13 rating, what that means in reality however with a determined tooled up thief?
Well, it means that the lock withstands all kinds of attacks for a bit longer than other locks rated with lower security ratings. 13 mm hardened steel is too fat to be cut with bolt cutters, the lock has some sort of freezing resistance, it takes longer to cut it with angle grinders (the rubber coating gumms up the blade), the lock has some picking and drilling resistance, etc.