1) Is the form of the verb used after 'so-', 'do-' & 'in-' the past participle or the genitive of the verbal noun?
In the few verbs where there's a difference I've seen both: 'Do-fheicthe' and 'Do-fheicsiona' (Dinneen).

2) Just a though. Perhaps it would be a good idea if a hyphen was used to connect all compound prepositions: i-dtaobh, ar-son, tar-éis etc. Many times I've had to make sure if what I'm reading is to be taken literally as a preposition + noun or is a compound preposition.

quote:

Is the form of the verb used after 'so-', 'do-' & 'in-' the past participle or the genitive of the verbal noun?

An chéad cheann de ghnáth, ach:

An réimír so- + aidiacht bhriathartha is foirm don rangabháil seo go hiondúil. [...] Corruair bíonn foirm nach foirm aidiachta briathartha nasctha le so-. Foirm ghinideach an ainm bhriathartha nó an ainmfhocail a bhíonn ann: sofhála, soghabhála, so-imeachta, soranna (ranna = seachfhoirm ghinideach ar roinn), sotheagaisc. -GGBC

Go raibh maith agat, a Dhennis.
I take it from that that both forms are still used.

I think only the first one (an aidiacht bhriathartha) is productive, however.