Maps are stored in folders with the same name (ish) as the map as you have probably discovered by now

. There will be a shed load of files in there if they are working. It is not unknown for the TomTom to delete the map files but leave the folder there.
For example on my 730 I have a purchased UK & ROI map and the original Europe map. I deleted the Europe map, (as it will never ever be used), with TomTom Home but it left the folder behind. No problem as the TomTom itself just ignores it.
One wonders therefore how the Europe files got deleted on the new card. in my experience the TomTom will only zap them if you tell it to. Did you check before you put the card in that the map files actually existed? If they didn't then you were conned.