No one ever said NIST didn't have access to the WTC7 steel, so we can take that strawman argument off the table right now.
And again, you're conflating two separate issues: Being able to identify which pieces of steel came from WTC7, and being able to distinguish individual pieces of WTC7 steel from one another. It is the latter that NIST was not able to do. Nor were WPI and Astaneh-Asl.
From WPI (bolding mine):
They had a piece of WTC7 steel, but they didn't know from what part of the structure it came.
From the New York Times:
Astanah-Asl examined an I-beam in the wreckage. At best, he said at a later time he might be able to get a rough idea from what part of the structure it came (and I couldn't actually find anything indicating if he was ever able to), but he wouldn't be able to identify which specific beam it was.
NIST needed to find a
specific beam out of thousands of tons of steel wreckage in which nothing was individually marked in order to provide the "physical evidence" you're demanding. And anyone with even the slightest knowledge of forensic engineering knows what an incredibly stupid demand it is.