The term bodhipakkhiyā dhammā has later come to mean a group of 37 qualities, grouped into seven sets. In the EBTs we do find both the term bodhipakkhiyā dhammā, as well as this group of 37 qualities, but they are not associated with each other. Or are they?
Well, not directly. When talking of the 37 qualities, the Buddha refers to them as “those things I have taught from my direct knowledge”. And when the “bodhipakkhiyā dhammā” (qualities that lead to awakening) are mentioned, this happens mainly in SN 48, where they are said to be the five faculties of faith, energy, mindfulness, immersion, and wisdom (which make up just one of the seven groups of “things that the Buddha has taught from his direct knowledge”).
But there is also mention of sevenbodhipakkhiyā dhammā: in DN 27, in Iti 82, and in Iti 93. Also, in some places in the AN (AN 5.56 and AN 6.17) we find mention of the bodhipakkhiyā dhammā, without specifying their number.
So I am now wondering whether it could be that we can see here traces of a transition of the meaning of the bodhipakkhiyā dhammā: Originally they were referring to the 5 faculties, and later their scope is expanded to the 37 qualities grouped in 7 sets. Can it be that the “sevenbodhipakkhiyā dhammā” that we find here refer to the seven sets of the later bodhipakkhiyā dhammā?
The preface mentions the circular interrelation (as opposed to the elementary linear), which is also referred to in Majjhima Nikaya 117, and how the interaction between sila/samadhi/ panna reduces the linear NEP to a circular dynamic. Thanissaro has elsewhere compared the progression from the linear to the more advanced circular interpretation to learning a musical instrument: first the individual notes are mastered, then they are put together to form a meaningful tune.
My recommendation is to develop understanding of the implications of Samyutta Nikaya 46.53 where the factors of awakening are divided into two groups related there to the elements of fire & water, passive and active, which is the dynamic (circular) perspective. Then from the simplification of the factors of awakening the other structures such as the NEP can be reduced to two dynamics.