Okay, so here’s my tentative timeline:
*1996-97: The metal TPM hero is constructed. The wonky emitter plate is the result of either an accident or innate to the prop’s construction.
The prop is molded and cast to create the painted resin dummies and stunts, and all feature the wonky emitter plate, but no pommel cube holes (for ease of molding/casting).
*2000-2001: The metal TPM hero is cleaned up for use in AOTC, since, in-universe, Obi-Wan either retrieved his saber from the pit, or constructed a near-identical duplicate to replace it (although the early post-TPM lore had him simply using Qui-Gon’s saber). The brushed/raw-ish aluminum parts are polished to a high shine, in order to match the look of the new AOTC sabers (Anakin, Mace, Dooku). A new emitter plate (possibly aluminum) is machined to replace or cover the steel TPM fender washer (which has likely rusted, akin to other surviving TPM props).
Resin TPM castings (or new castings made from the old molds) are now chromed instead of painted, and again serve as dummies and stunts. Ewan favors these lightweight castings, and the metal hero mainly appears on Ewan’s belt in publicity/reference photos.
*2003-2004: By this time, the metal TPM hero has gone missing/into private hands. To give Lucas options in preproduction for ROTS, the prop team either modifies a second metal hero (possibly created for AOTC), or, more likely, machines an all-new prop, using the resin TPM/AOTC castings as reference. The primary design difference, of course, is the famous salt-shaker emitter cap.
As before, resin dummies (with varying levels of detail, for the stunt performers’/actor’s comfort) are made based on this design. The resin stunts are used in early duel practice sessions, and the metal salt-shaker hero is worn on Ewan’s belt for costume/set photography test shots.
Eventually, Lucas decides that Obi-Wan will simply wield the Alec Guinness-style saber from the very start of the film, and the salt-shaker is relegated to non-canon obscurity, appearing on tour and in publicity photos/StarWars.com articles (often mistakenly labeled as the TPM and/or AOTC version).