Jamie wrote:
Thank you both for your input.
Admittedly my research was limited to grammar textbooks and other books on learning Irish e.g. Teach Yourself Irish - Myles Dillon (1961), Modern Irish - Michael O'Siadhail (1989), First Irish Grammar - Christian Brothers (1920). As well as the grammar guide on nualeargais.ie. My apologies if my claim of having done research was misleading. I will definitely check out Diarmuid Ó Sé's Gaeilge Chorca Dhuibhne. Now you mention it, prose and novels by Kerry authors would have been a wise choice of reference, thank you for the suggestion!
Thank you again and any further input on where I can do more research on in future is more than welcome.

You can order GCD from here:
https://shop.dias.ie/product/gaeilge-chorca-dhuibhne/It is 35 euros, and all in Standardised Irish, although the examples sentences are all in Kerry Irish. It is the "mother ship" as regarded Munster Irish - and the most comprehensive treatment of any Irish dialect. I believe an English-language edition (much needed) will come out one day, but it has been just about to come out for over a decade, and so it is not worth waiting for...
If you want to search for examples in Kerry authors, you could sign up (for free) at
https://focloir.sketchengine.co.uk/run.cgi/index, where you can search the Nua-Chorpas.
The fundamental upshot is that slenderisation in the dative is only a feminine thing, and even then not often found nowadays. Peadar Ua Laoghaire occasionally had it, but not always, so even in his day it was on the way out...