Glad to hear Nan's just a round rat lady. One litter at a time is enough work!
Does it look like they'll all be solid white, so far as you can tell? Even the smallest of distinguishing marks can be helpful. Otherwise there's a lot of, "Hey! Uh... Whichever one you are! Stop chewing on the duvet!" Do you find that happens much, or is it easier for you to tell that many identically-coloured rats apart? (Hannah had eleven babies; food colouring markings on their tails helped tremendously while we rehomed them.)