I noticed it on a recent reservation reminder email as well, although it's definitely not consistent across all corporate AWDs. I won't specify which AWDs did/didn't trigger the warning but to me it's clear that some are being watched more closely than others (guessing it's especially the ones with unique discounts or special terms like no one way drop fees).

Thankfully I always retain old company IDs/badges and business cards from prior jobs so I'm going to stick with using only the ones where I can provide "proof". Best practice for me when traveling is to always have my mini tumi pouch (the old soft pouch DL amenity kits) with all forms of company affiliation in case I'm ever asked at a hotel or car rental.