We don't use the vet for scanning as they don't do enough of it to be truly accurate. There should be someone in your area who scans and will do thousands of sheep a year. Most of them will tell you single, double, triple, quad and XXXXX not to mention the empty ones, but be warned, I used a new scanner this year as my chap was not available when I needed him and he scanned 30 ewes as empty - I didn't trust him so kept them and 22 out of the 30 lambed!
When my vet scans the dogs they will only say 1, none or more than one.