I'm curious if this is happening consistently. When we were there last year we bought 6 mugs all at the same time (one transaction at a single register). When we filled the mugs for the first time, we noticed that some of those mugs had the standard 2 week date; 1 or 2 had a date 4 weeks out; and 1 had a date 6 weeks out. I have no idea why or how we ended up with 3 different expiration dates on mugs that were all bought at the same time and activated by the same person.
You got a date of 4 weeks when you bought your mug but that doesn't necessarily mean everyone is getting that.