If you edit the save file and put a negative amount of credits, data and data multipliers, you get negative values. Also, if you put extremely large amounts of data by editing the save file (e.g. 1e+33), it doesn't appear as "1000 QB" but rather stuck on 0.
Alright, since these bugs are artificially created, i will not investigate or try to fix them, since they will not occur in the expected normal flow of the game!