I really think you are causing yourself undue stress by over thinking every tiny part of this. When she says "you are advised..." it doesnt mean YOU MUST DO, and it doesnt mean you are doing anything else wrong.
My test result page was not stamped by my vet, but if it will make you feel better to have her stamp it, then go ahead. By stamp, they just want the vet's address stamp (the one they will use on the EC998 form). If nothing else, it just ties everything together.