Same could be said for any religion even christianty whos to say that the translations were right or that the ones who found the original text were not tained?
I think all transfers of information involve loss of integrity, be it translation or simple copying, its the 2nd law of thermodynamics, entropy and decay, if you use a photocopier to copy any document and then copy the copy repeatedly, eventually and surprisingly quickly you will have an illegible mess, humans are much less efficent then machines so i have no doubt modern Christianity is not the same as it was one thousand years ago.
Plus of course people in authority deliberately edited the Bible too, including certain texts into the canon and rejecting others, not to mention the liberal translations etc...
Anyway...you will have to resurrect your religion from a limited pool of information, I guess that means a lot of study and dedication, the druids, I believe but I am sure you would know better, had various functions and some specialised in certain areas, the underlying theme in my view was about caring for the society they lived in and because of those early agrigarian times that involved caring for the land as well.
I personally am very keen on druidism and as it started in Britain (probably) it is a part of our heritage that is largely ignored, except by academia, we instead concentrate on graeco roman culture, which is not our heritage really, only a contributor.
Good luck then, I salute you!