shared souls perhaps? real syaoran used the magic diferently then ccs syaoran. ccs syaoran uses parchemnts with elements written on them, right? and also, real syao's magici circle is the "laisin board" symbol, so it more over the shared souls thing thn anything
Actually, CCS!Syaoran can do magic without his ofuda (the parchments), he's been shown to a few times, if I remember correctly, and there was even one rare time where he released a Clow Card without using his sword either, and just held it between his 2 forefingers. I think it was the Dash....? He could even use his ofuda without the Jian sword too (an example would be when Eriol trapped him with the strings). I guess he is capable of doing his spells in different ways (Mind, I'm using examples from both manga and anime).
Also, CCS!Syaoran's magic circle IS like the "laisen board". It's the Rashinban. There' no doubt. R!Syaoran used his CCS counterpart's magic. Whether he is CCS!Syaoran himself, is yet to be solved.
R!Syaoran could be whoever at this point, all we know is the above, and that he's got Clow's bloodline as said by FWR, probably by a different Clow Reed, who knows? And IF time is different in each world/dimension, doesn't it mean that you grow at a different rate too, considering the timeline? So if a person goes to another world, to they still have the growing rate of where they were originally from? And is not fact that R!Syaoran was stuck there for 7 years in the tube. People just calculated it. Plus, we see that he may be younger then Clow!Syao...
...........I'm going to have to join the group of people who are confusing themselves.....I need a rest.