This. My 14.2 is also in a 40" girth, but needed a longer girth for the borrowed saddle we used when his was with the saddler.
His old 38" girth is now on a friends 12.2 (technically still fit, but was only elasticated on one side which didn't suit his shape and we had a bit of slipping).
Can't comment for the particular horse height - but maybe this helps.
I had two girths for my 13.1hh NF X TB- a regular & an extra big one (and a spare really small one from when I got him and he was underweight). The extra big one would do up to the top of the billets - but I had to use it when he had too much grass and was a bit of a fatty.
I now have a 16hh TB who uses that 'extra big pony' girth I used on the 13.1hh. Fits him at the bottom of the billets. So you have a lot of leverage in fit - not saying this will apply to every horse, but if you choose a size within reason and logic then there is a good chance of it fitting. if your unsure, just keep the tags on while fitting it and keep the receipt.