Good question. I really have no idea. I assume, if she drew them and not the Tech,mshe knew which was which. Also, there may have been a different quantity of liquid in the syringe or a different color.
I would call and ask them. Your right to do so.
I ended up asking a tech at the vet hospital and she said they have two safety measures in place there. One is that they keep one of the stickers for the vaccine on the syringe until it is administered and then they transfer it to the pet's medical file. The second is that they put an R on the end of the syringe containing the rabies vaccine. I don't remember seeing the sticker or the R, but I trust that it was done since it is standard procedure there. My mind was put at ease after I talked to her, so I'm glad I did and thought I'd come back and share the info. in case others ever had this question. I'm sure procedures differ at different vet hospitals, but I think the sticker procedure at least is pretty standard.
Glad you called and put your mind at ease.
Thanks for the update!