How many do you have open? Should I be concerned that I have so many open? I know I can’t try them unless I open them but I like to see what I’m missing! Still looking for that bestest one.
Booze or Snuff? 
But seriously…I always keep them closed in-between sniffs.
I have about 11 open at a time regularly. I have never had any problems with snuff going bad. I have had this many open for months and have not had any trouble. This is assuming you do not literally mean keeping them open.
I have had around 50ish containers that I opened this past year (and are still in-use), but obviously, closed, when not in direct use. No freshness issues, until I am down to the last few pinches. Big containers, like 100g bags, go in airtight metal canisters for storage , after being decanted into 10g or so containers.
I have about 150 opened containers.
Thanks for the feedback everyone. I was hoping to hear that I should expect little if any lose in freshness. I do follow the advice given in other threads about decanting to smaller containers for filling my daily uses dispensers. Then resealing original container. Thanks again for the (implied assurance) that I should just enjoy my snuffs and not worry about it fading.