In the SI you mention, otherwise known as The Parish Councils (General Power of Competence) (Prescribed Conditions) Order 2012, Article 1 defines the meetings thus:
Citation, commencement and interpretation
1.—(1) This Order may be cited as the Parish Councils (General Power of Competence) (Prescribed Conditions) Order 2012 and comes into force on the day after the day on which it is made.
(2) In this Order—
“annual meeting” means a meeting of a parish council held in pursuance of paragraph 7(1) of Schedule 12 to the Local Government Act 1972;
“relevant annual meeting” means an annual meeting that takes place in a year of ordinary elections of parish councillors.
The conditions of eligibility in the schedule to the SI are defined as:
Conditions of eligibility
1. The council has resolved at a meeting of the council and each subsequent relevant annual meeting that it meets the conditions in paragraph 2 below.
So you are correct that eligibility is not revisited annually and the power is retained until the next ordinary election, regardless of changes of circumstances of the council.