The liners Westwood list look like they are the equivalent to boring to around +120. So if a bore was at a worn +100 it could most probably still be bored to suit the sleeve.
Whether or not one can go +100 (if one could get the pistons) would I think be determined by whether the spigot was still strong enough (I guess it probably is?).
The Westood sleeves are 2.756 id which is nominally the std bore, but the size probably allows for boring/honing after fitting the sleeve, to suit the pistons. It will reduce from it's supplied size, due to the barrel/sleeve interference fit.
I had my sleeves honed to remove some post seizure scratch marks and prior to fitting some new JP pistons. I asked the reconditioner about boring them to fit oversize pistons if honing did not remove the scratches, he said it would be "marginal" and recommended new sleeves as a safer option and it would not cost me TOO much more.
He would have bored the sleeves to plus 020 if I had asked him to, which would leave the wall about 060 thick, maybe a bit less.
Another concern he had was as another company had fitted the sleeves originally he could not be sure if they had the correct interference fit and if not, then boring them might cause them to slip in service.
I've seen advice that sleeves can be as little as 050 thick but I've not heard experiences about anyone trying that on an A10. if it's ok to do that then I guess the Westwood sleeves could be bored to +020.
This topic on sleeves might become more relevant as we all wear our barrels out to the limit! (whatever the limit is...)
This is the westwood page for A10.
http://www.westwoodcylinderliners.co.uk/index.php/products/marques/liners/bsa/