If it's a week, all of them. Start worrying when it exceeds a month.
I've found that Mexican Pinguicula handle shipping for extended periods rather poorly. They are very quick to etiolate, this usually happens within a week. I've had no problem with other genera for up to 3 weeks though. Just keep in mind that if the plants are in transit for over a week or 2, they will be very soft from being bagged in high humidity and kept in the dark for so long. They will usually need higher humidity than normal for a few weeks while they acclimate.