I think the use of the term arc is possibly better that corridor. The two arcs, if I have understood correctly, are the result of "triangulating" data captured by two satelites using time codes. What is not clear is whether the last "ping" cannot be precisely positioned on these arcs which then possibly means that they are indeed corridors (i.e. arcs with a width corresponding to precision, with the points sighted being the limits of accuracy at say 2 std deviations.
Assuming the aircraft was flying in a roughly constant direction, I suggest that the actual last position can be estimated with a further arc being when the a/c ran out of fuel or landed and was shut-down, which clearly must have been around or after 00:11Z. This suggests it could well be towards the western end of the northern corridor.