Tom's tie work is cost-prohibitively inconclusive.
If you take five ties from random places - one from a bus driver, one off the rack at a store, one from a floor manager at Tektronix, one from a TV repairman, one from a thrift shop, for instance - and test all of them against each other, then test the Cooper tie, then you have usable results.
Without a control experiment, the case can be made that the lab screwed up. Or the FBI didn't store the evidence properly. Or that all cloth gathers all elements by diffusion or some shit. Anything a defense attorney can sell to a jury.
I still don't know why Tom is willing to discount sulphur and lanthanum as matches and lighter flint from smoking, but virtually nothing else. The guy had a bomb. Real or fake, the components were there, in contact with him like his matches were. His hand was in that briefcase a whole lot, and 50/50 that he used that hand to take off his tie. Casual transfer, they call it.
Yes, some of those particles may come from the owner's work environment. Yes, some of them likely come from matches. But some of them likely come from that gadget he put together. This tie has layers.
Figure out which come from the "bomb," subtract them from the McCrone data, and the work environment view sharpens.