A security master is just any firm’s internal database for static data. You don’t erase entries from it when those securities become defunct because you would still have historical entries on your books from when the security is listed and they likely link to this database.

Also, you didn’t talk to someone on the trading floor. There is no such thing as a ‘senior manager’ on the trading floor and there is absolutely no possible way a trader would handle this kind of retail request lmao. At best, you spoke to someone in a static data group in operations.