Versuch, no daggers for you my friend, just the compliments of the season.
Thank you for posting up the magneto and engine information, which gets closer to the mystery of the CSE 12- 12S and CSE-ES magnetos, which I think were custom builds for Napier, the first time I have seen the engine designer dog wag the magneto manufacturer tail !

My guess is that these magnetos were constructed on a similar principle to the two crankshaft Dagger engine they were placed on :
a central engine driven spindle geared to two new spindles driving through two piggy backed coils. It would not be hard to do this if you shifted the distributor into a separate device. What about the points. Perhaps they yin-yanged around a single lobe arrangement, necessitating a larger points cover. I have held one of these points covers in my hand and it is much larger than the standard points cover on the standard CSE magneto.

To prove or disprove this theory the driving ratio from the engine to the twinned magneto is required, then an assumption that the lobes opening the points were the usual 4 lobe arrangement, then follow this gearing arithmetic through to the distributor and engine.

In simple terms the Napier Dagger, with 48 spark plugs, had the equivalent of 4 x 12 cylinder magnetos stuck to it, optimized into 2 x 24 cylinder ‘custom’ magnetos.
It seems quite brilliant, typically Napier, typically introducing 200% more dependency on nothing going wrong….