I'm not editing the article regarding the numbering of the Fort Smith section of I-540 because it seems the writer may have been there more recently.  However, IIRC when I traveled that road shortly after the newer part of I-540 was completed a few years back, the exit signs and mileposts WERE renumbered to be consistent with the new road (i.e., from Oklahoma line north), though local billboards still had the old exit numbers.  Perhaps an AHTD re-signing project erroneously restored the original exit numbers and mileposts?