R4s with a time bomb are mostly easy to spot. They have a year on the sticker (2017, 2018, 2014, etc.). Or the instructions tell you to turn back the clock on your system by a year or 2 or more.
It you find a R4 that doesn't have those blatantly obvious tells, you got yourself an R4 that isn't programmed to give you the middle finger in a year.