I suspect that you are perhaps correct on both counts.
The publication stats do indeed state Nua Eagrán (Bog) ; 1985 which, at face value, would imply that this was simply a 1985 softcover reprint.
I’m always confused, however, when the term ‘Eagrán Nua’ is used. I would take this to mean that the edition has been revised rather than a simple reprint (in which case I would expect to see the word ‘Athchló’).
Then it continues on to state ‘An t-Eagrán Nua Seo 1999’ for the current version, the preface of which indicates that Eagrán Nua 1999 is indeed an update. Given that the same terminology is used (Eagrán Nua), I suspected that the 1985 Eagrán Nua would also be (as well as a soft cover edition) a new revised edition.
Do you have a copy of the 1985 edition Labhrás? Is there an updated preface marked 1985? I actually haven’t read the 1999 version yet (though I do have a PDF copy) so I’ll be interested to compare the changes in the 1999 update to the original edition. I can’t imaging that there were too many changes.
You might also be right about Nua Chúrsa not being a Grammar book. I will check that out.