In short if Gotprints or whomever decides to print a shirt with the aggy (misspelled on purpose) logo and they dont have a license, then yes, they are responsible. If a license holder, someone that could possible pay thousands or millions a year in royalties to the university finds out that someone is printing and selling without a license, yu can bet they will be reported.
Besides, a local license if very easy to get and inexpensive..why not just get one and then sell to all the bookstores in town?