i asked today at work which gave me no new information
the dots which are on steel wheels mark the high/low spot on the wheel and there is a dot on the tire which marks the high/low spot on the tire the dots are matched to reduce the amount of weight which need adding after the balancing. Alloys dont usually have this problem because they are usually pretty spot on unlike steel wheels which are just lashed together and then welded so alloys dont usually have high/ low spots on them.
the alloys they put on the cars at work dont have any marks on them so i am unsure what the blue dots you had on your old alloys meant.
if you really want to check i would just do what you said and ask for the job number and check with nissan GB they should be able to tell you
hope they are new and they havent tried to fob you off with some refurbed ones