Nice one.
I think I'm getting where you're coming from.
So, when the rods were submitted on 3/15/64 they were already marked with Warren Commission Exhibit Numbers 275 and 276
No, the Warren Commission Exhibit Nos 275 & 276 had already been assigned elsewhere (during Mr Robert Oswald's WC testimony in February), and the assigning of Ruth Paine Exhibit Nos 275 & 276 was still eight days in the future.
The rods submitted to the lab 3/15/64 were marked (for whatever non-WC-related reason) with the numbers 275 and 276. This is what
necessitated the later blatantly contrived
creation of Ruth Paine Exhibit Nos 275 & 276. The 'marking' of two curtain rods as such was the entire point of the testimony session in Irving 3/23/64