Furthermore, welcome to the forum!
Quote:
Originally Posted by keisentraut
 P1 was done to 2M and 50M, so the smallest factor who could be missed would be 2*2655361*50000001+1 which is also around 48bits. Most likely larger numbers would have been found with those bounds.

To be a bit nitpicky, the smallest possible missed factor is \(f := 265537167455123 = 2 \cdot 2655361 \cdot k\), where \(k = 50000201\), because if \(k\) would not be prime, it would have been found with a smaller bound. Also, \(f\) has to be prime, otherwise it would have been found earlier.
Quote:
Originally Posted by keisentraut
 If you already did n ECM curves with a given B1 bound, then the chance that the (n+1)th will find a factor is lower than for the very first curve, isn't it?

Unforunately, that's the Gamblerâ€™s Fallacy. I hate that, too, but you cannot ignore it.