The case of one who shechts in 2 or 3 places - Tosfos understands Rashi to hold that if a small cut precedes a large cut (rov), it will prevent the large cut from being clearly discernible (mefura'as).
But it's clear from Tosfos that if there are two cuts of rov on the same siman, that would be fine, if not for the fact that it was already rendered pasul earlier. Why should two cuts of rov be good- if a small cut affects a big cut, certainly a big cut should affect a big cut and vice versa.
The Maharam asks your question.
The Rashash answers that one cut only affects a different cut and stops it from being considered Mufra'as while the knife is still in the Siman. However, after the knife has been removed the cut joins together and a further cut can be Mufra'as. Therefore the second cut would be considered Mufra'as, but the animal has already been Nifsal.