> the first sentence describes plotting in different projections, so we are referring to the same ones here

Not really, we are actually using *four* different systems in all:
 * The data sources are on two different rotated-pole projections (and margin lines are in one of these).
 * The text + gridlines are in true-lat-lon.
 * The plots are displayed in true-lat-lon and north-polar-stereo.

Strictly speaking, the 'arrows' are also sized in display-points which is different again.
So "both" doesn't really cut it any way (!)

I do agree "described in" is pretty weak, though!  I'll try and improve this...