I believe you. I'm just a person who likes musicals and plays and goes to the theatre a lot. You and Chromolume actually work in the business and obviously know tons more than I do.
When I saw Mame in '94, "St. Bridget" was not in that particular production -- I've got the playbill right in front of me now. I've been posting on ATC since '97. On one or two occasions in the last 25 years, other ATC-ers have apparently seen regional productions of Mame in which "St. Bridget" was not performed and posted about it. I read those posts. That may have been years or even decades ago. I wasn't trying to make some sort of definitive statement about what is licensed or what isn't. However, I seriously doubt that anyone would deliberately misstate that type of information on a message board.
Over the years I've seen any number of musicals at small regional theaters in which various songs from the original scores were not performed, key songs that told the story. I don't know the reasons, possibly time constraints. The Marriott in Lincolnshire is notorious for doing this, to name one Chicago area theater.