Token - Prepaid : .5 GB (9 Available"

They're assuredly tokens that were given by the reps for some reason, whether in anticipation of some testing that was going to be done or even as compensation for an outage or other issue, including something widespread that affected a lot of people.  

Two or three years ago there were two widespread, short lived outages for which they compensated people with 3GB of token data for each one.  One was in the evening on January 1st (2019 maybe?) and the other was either a few months prior to that or after it.  You weren't a customer at that time, but I'm just using those two things as examples of what they sometimes give data tokens for.  

It's also possible that there was some type of glitch in the system that has been giving you one each month.  The old daily refill legacy plans would get one free token per month, and the system could just have mistakenly given you the same.  

Enjoy em.  It's the magical digital gift horse.  LOL.  😁