SRAM eTAP cassette compatibility I'm having trouble understanding SRAM road component compatibility "map" as they call it, specifically the cassette and rear derailleur part.



For example, the PG-1130 cassette has no black box marker for the 11-28 size. What exactly does that mean? How can specific casette sizes be incompatible with ANY derailleur size (neither medium nor short)?

In my specific case, I'm upgrading to eTap and since I have a spare new PG-1130 11-28 cassette with PC-1130 chain, I was going to use that, but now after checking the chart it does not make any sense to me. Anyone could explain this?
My interpretation: dots indicate availability. Bars under the cassette sizes indicate compatibility with medium and short cage derailleurs.

I assume in previous years SRAM made a 11-28 PG 1130 cassette.