they sat in the quiver all year long? I have heard that humidity can cause them to dull.

i don't know if that is true or not. But i do know that if i am using the same brand,weight etc head this year as last, that last years heads become my practice heads for this year

Every year before I head out bow hunting I check my Snuffers that have been in my quiver all winter and summer and usually I'll have to touch them up a little with my crock sticks. It don't take long but I like to get that fine paper edge back on them. Just from taking the same arrow in and out of your quiver can dull them a little after a period of time. Its a good practice to get into, certainly not a bad one!

I always check them, if they need it, I sharpen them.

Amen, or replace them.

And yes, killdoe, air itself etc can oxidize a broadhead and dull it as well as continuous in and out of the quiver during the season.

Better safe than sorry when it comes to broadheads. It could very well mean the difference in a trophy of a lifetime.

I always touch them up just before hunting season

No scientific evidence that I know of to support that. Sure is a good ideato check them anyway every year. Better safe than sorry, right?