To me it does seem that the "experts" are only making educated guesses about the language. Through trace evidence such as place names and modern forms of Brythonic languages. Britain is a land of mongrels if you want to put it blunt there has been so much movement of peoples that I doubt very much any expert has the definitive answer on language origins. One question can a dead language be truly revived or will it always just be a modern interpretation that noone can contradict because it was dead as a spoken language?
If you want experts in sheep counting speak to a New Zealander. Saw one on countryfile once with the hobby farmer presenter and she pretty much counted up the flock in a couple of seconds in a field. As far as counting goes is a base 10 system or a base 5 or whatever base any quicker? I know we are all "trained" to use a base 10 counting system but is that really the fastest one? Once learned could another base number be faster? Afterall the Yan, Tan, Tethera counting system seems to be base 5. I suppose the one you're used to is the fastest for you.
a lot of tribes round the world ive worked with use this system where they count to twelve on each hand, so 24 in total. they work with their thumb and count the joints rather than individual fingers. so thumb on top fleshy bit of index finger is 1, second fleshy bit is 2, third fleshy bit is three, thumb, top fleshy bit, second finger is four. etc. this is something that i often do because you can count a lot more with one hand that way.