Credit score vs. credit history--an issue for our kids?

My son’t in college and has a Discover iT card in his name. Low credit limit but using the card at least once a month and paying the balance quckly has helped boost his credit score. See:

https://www.discover.com/credit-cards/student/?ICMPGN=PUB_HDR_CARDS_STUD_IT

^^The federal Credit Card Act of 2009 mandates that you must be 21 or have a full-time income to get approved. The tightened rules mean most college students can’t qualify for student cards on their own.

Still can’t figure out how D3, at the age of 17 in 2014 was given a cc by Wells Fargo. I believe D2 received hers from WF after 2009 also. All has worked out well but I’m wondering if there’s some loop hole to this mandate.

Our D got a CC from AmEx when she was shopping at Costco with me. At the time, she had NO job and has never held a full time job. She was and is over 21.