You are probably more likely to spontaneously rearrange your constituent atoms into cheese or something than to generate the same random 16 bytes twice, assuming a new number needs to be generated only once for each package of code signed. If there was one needed for each packet on a network or something it might be different.
In any case, this risk is orders of magnitude lower than the risk of someone leaking your list of past numbers, especially when they're this valuable.
Even worse, if you are using a list to eliminate the possibility of repeats then you aren't generating a perfect random distribution any more. The possibility of repeated numbers, however small, is explicitly allowed.
In any case, this risk is orders of magnitude lower than the risk of someone leaking your list of past numbers, especially when they're this valuable.