I am looking at the Atmel SAM D20E / SAMD 20G / SAM D20J data sheet (Atmel-42129P-SAM-D20_Datasheet_Complete-09/2016), and specifically at Table 7-1 Port Function Multiplexing.
I was under the impression that for each SERCOM/PAD it would only be routed to one pin under "function C" (SERCOM) and one pin under "function D" (SERCOMALT).
In the table I find two sets of entries for the SERCOM4 PADs (PB08-09-PB10-PB11 and PA12-13-14-15). Similar duplicates exists for e.g. SERCOM3 and SERCOM5.
I have a hard time believing such a blatant error would pass through corrective reading before publishing, so what would be the point in "duplicating" the routing in this way, having the in- and out-put of one SERCOM on several sets of pins?
EDIT/PS: I confess not having read every word of the data sheet yet. On my way, though...