Is this not a regional thing where both "Tá mo chuid éadaí sa gcás" and "Tá mo chuid éadaí sa chás" are valid? (The first one is rejected)
The first one should be accepted, yes. It's standard in Connemara, and now accepted in the official standard, just as lenition in the dative is.
In past versions of the Caighdeán, nouns following den, don, sa, and san could only be lenited. The 2016 version also allows eclipsis for either (den and don) or (sa), so both sa chás and sa gcás should be accepted here.
Inquantifiable yes. But also general plurals, too mo chuid leabhra (my books)
I was sure, that I'd seen "m'eadaí" somewhere, couldn't find it, looked at google, and the first place was DL ;-)
Now the instance with "her putting my clothes around me" is maybe different use than "some amount of clothes in general in a suitcase". Still question is would it be wrong or not / is it worth a report?
On Google "mo chuid éadaí" gets five times as many hits as "m'eadaí"
Yes, that one should be mo chuid éadaí. m'éadaí would only be used by non-natives.
I first learned it as "mo chuid éadaigh", ie genitive singular, which gets about twice as many Google hits as "chuid éadaí". It was rejected when I put it in an exercise. I reported it at the time but I haven't tried it again to see if it's now accepted.
I've just taken a look in Ó Dónaill and it gives examples such as: 'a cuid éadaigh' Her clothes. 'Ina chuid éadaigh' in his clothes. In fact it doesn't include a single example using the genitive plural 'éadaí' so it seems you are correct.
Pota Focal does give a couple of examples - "cá bhfuil do chuid éadaí?" & "cuir ort do chuid éadaí" - under the head word "éadach". Perhaps the "éadaí" usage is a more modern one (influenced by the English plural?) In any case, it would seem that both forms should be accepted.
The FGB examples may provide illumination:
- Mo chuid éadaigh — genitive singular (uncountable noun)
- Mo chuid bróg — genitive plural
- Do chuid leabhar — genitive plural
- Do chuid eolais — genitive singular (abstract noun without plural form)
- Ár gcuid saothair — genitive singular (abstract noun)
- Ár gcuid trioblóide — genitive singular (abstract noun)
- A chuid fear — genitive plural
- A chuid saighdiúirí — genitive plural
- A gcuid mac — genitive plural
- A gcuid aithreacha — genitive plural
It looks like Mo chuid éadaigh is akin to Mo chuid bainne in that they’re both uncountable, and thus should take the mass (i.e. singular) form rather than the plural form — I think of mo chuid éadaigh as “my clothing” rather than “my clothes”.
Dinneen’s 1904 dictionary has éideach (meaning either “clothes” or “armour”) with a reference to the éadach entry, but unfortunately there is no éadach entry, not even in the “Some Additions and Corrections” section. Éideach had its plural forms identical to its singular forms, so e.g. mo chuid éidigh could have been either singular or plural, which might have influenced the acceptability of mo chuid éadaí.