If you look at this ECM report for M1277:

https://www.mersenne.org/report_ecm/
you can see ECM up to 60 digit level is done and almost half of 65 digit level. That means the chance of a missed 60 digit factor is well below 1/e~37% since the half 65 digit level also further rules out missed 60 digit factors.

The chance of a missed 55 digit factor is much much lower again, and so close to 0% it would be a miracle if one was found. 55 digit factor is ~ 2^183 so you can see why there is no idea trial factoring between 2^65 and 2^80 ?