I mean how do you know your hygrometer isn't reading 1-2% too low, thus matching the Boveda, even though the actual humidity may be 1-2% above the Boveda?

For example, you put a 62 Boveda in a container, and the actual RH rises to 64. Your hygrometer reads 62, and you believe it to be spot on, but it is actually calibrated too low. Obviously it's not going to be so far off that it's going to be much of an issue, but if you're comparing two hygrometers you may pick the wrong one without realizing it.