Boys got new reflecting vests today. The salesman said size L (large) should be fine for retrievers as XL is for the really big boys.
Apparently male flatties are big boys.
The vest was very tight for the boys so I will need to get them size XL and let girls ware these extra ones in case they need new ones.
But the price €4.99 for one vest is a really good price. Especially as the reflecting of the vest really works well. Just tested it today bicycling in the dark forest after 7PM and it was snowing a bit.