fairly standard practise with many programmes, you will find that programmes that have long stay properties tend to have limits. Adagio was only very recently added to A-Club so things might need clarification.

I would hope that points up for the 30th day should be credited in those circumstances.

They are not saying you can't stay longer than 30 days, they are saying you are not getting the points. As A-Club elite status is awarded on a nights basis, unlike for example Hilton Honors stay basis, I assume they want to limit too many members achieving elite status through one long stay at Adagio.

You are right the wording in the T&Cs is ambiguous.