Benedict, please accept my profuse apologies for overlooking to post this response of mine to this question that you made over three weeks ago. So many things got in the way that the matter completely slipped my mind.
Yes, of course, the backshifting of tenses particularly applies to the verb in the relative clause of a sentence, so the reported form of the sentence you presented would be correct only if the past-tense verb
"were" is solely used in the relative clause and the past-tense verb
"are" is not presented as an alternative. The reported speech form of the sentence would then take only this following backshifted forum: "He
said the program
was available to members who
were delinquent in their payments before the March 10, 2021 cut-off date."
You must also keep in mind that
formally, the above backshifted form of the reported statement needs the subordinating conjunction
"that" to clearly indicate that the clause needs to be backshifted, with the verb
"are" in the reported statement getting backshifted to
"were" as follows: "He
said that the program
was available to members who
were delinquent in their payments before the March 10, 2021 cut-off date." I must emphasize though that in practice and for immediate articulation, the subordinating word
"that" is typically dropped after the reporting verb "say" for what was spoken, as follows: "He
said the program
was available to members who
were delinquent in their payments before the March 10, 2021 cut-off date."
The word "that" actually has many functions and uses in English and this is most likely why this basic aspect of reported speech remains confusing to a lot of English learners. To get a better handle of what "that" does, you may want to check out Thoughtco.com at
https://www.thoughtco.com/uses-of-that-1210017 for its very helpful discussion of the "Proper Usage of 'That' in English."
For a more exhaustive discusssion, read the Forum's 3-part "A full-dress review of reported or indirect speech"
