False positive for Oxford comma for pairs

**What got flagged?**
> It's A or B, B or C, D or E, or F or G. ■■ An Oxford comma is necessary here.

**Why is this incorrect?**
Expressions `A or B`, `B or C`, `D or E` and `F or G` are *self-contained*, and thus roughly equivalent to `W, Y, Y, or Z`.

Reproduce the reported sentence and trace the Oxford-comma check that flags it. Confirm that the four paired expressions are treated as self-contained and that the false positive no longer appears, while existing Oxford-comma behavior remains covered.

Written by the indexing model from the issue text.