To What Degree can the Abhidhamma be used to reconstruct EBTs?

And can certain texts be eliminated from consideration as EBTs because they reflect Abhidammic concepts?

The short answer to the first question is “It depends.” If we look outside of Theravada Abhidhamma and look at the Sarvastivada tradition, there was a clear development from early Abhidharma to later philosophical Abhidharma, and then to treatise writing by scholars who debated each other. The constant trouble with sorting that out in Indian religion is the lack of any objective history of who wrote what when. History wasn’t a strong suit of Indian civilization. They preferred myth.

Scholars like Frauwallner have done their best to sort out early, middle, and late era Abhidharma and compare them each other. There’s a collection of his writings on these topics in English titled Studies in Abhidharma Literature and the Origins of Buddhist Philosophical Systems. He summarizes the basic conclusions a person can reach looking at the extant Abhidharma collections.

The open question that’s difficult to answer is: How old were the earliest Abhidharma texts? And an equally thorny follow-up to that question is: How much did those early texts get edited over the centuries as newer ideas developed?

Still, I think the early strata is similar to the avadāna literature. It may not have been taught by the Buddha himself, but it may go back to the first generation or two of disciples. Or, it might have developed a couple centuries later. It’s difficult to know since it’s too far back in time to find objective evidence one way or the other.

Your second question is easier to answer. There were some clear developments of Abhidharma philosophy over time, evidence of which exists in Sarvastivada Abhidharma. The classic example is the reworking of the realization of the four noble truths. Instead of destroying the asavas, theory developed that the anusayas are destroyed. There were also sectarian divides over precisely how the realization happened: Were all four truths realized at once, or was it one at a time? When we see these types of ideas in sutras, I think it’s obvious the sutras were edited or written later in Buddhist history. That’s one of the easier ways to sort out EBTs. Indeed, when scholars attempt to discern which sectarian school a given sutra belongs to (it’s not always obvious with Sanskrit finds and Chinese translations), they look for tell-tale signs in the form of known sectarian views and ideas.