tenses - Which one would sound better : "are used" or "being used"

This question is similar to this one but I'm trying to decide the tense to use in here : I often use "is being" and "are being" in my sentences. Is it correct grammatically?

The xxxs which will be used in the xxx unit, must be defined in this
section before being used in the programs.

or

The xxxs which will be used in the xxx unit, must be defined in this
section before they are used in the programs.

Answer

At Google Books:

"defined before being used"

About 694 results

"defined before are used"
8 results

The first seems to me more general: as it only uses non-finite verbal forms, it can adapt to any time, from past to present and to future. The 2nd follows the idea of flattening everything to a narrative present tense.

The first is clearly more liked and, IMO, more elegant.

Now, if we go to the fuller clauses:

"must be defined before being used"
About 64 results

"must be defined before they are used"
About 919 results

which to me indicates that both are accepted. I still prefer the first.