Irish

They don't mention any concrete sound changes or phonological changes. For example, it seems the suffix on some words was shortened going from Common Celtic/Proto Celtic to Primitive Irish (kattus to cattu), something which doesn't seem to have happened in Common Brittonic from the same period.

The -s was definitely still preserved in Primitive Irish at least in the early period, and it lingered on in Old Irish in the form of initial aspiration.

I see, thank you very much. If I may ask another question, is that why we find both "maqqas" and "maqqa" and then "maqq" attested?

I don't know. Are they all nominative singular?

I believe so.