The "up to ecbdata->nparents" is Johannes in cd112ce. But you
are looking at a wrong code, I am afraid, if your original
question was about the combined format (there is a comment about
the codepath dealing only with two-way diffs by Johannes, above
the part you quoted). The output for combined diff is coming
from combine-diff.c:dump_sline().
Combined diff output logic pretty much guarantees that you never
will see plus and minus on the same line.
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