Recently, I hand-loaded some Alliant Reloader Powder I had in my lower cool dry garage cupboard.

It was for my 7mm Rem Mag rifle and discovered the powder lost some of its potency. It was an opened can and had about a half pound left. All of the loaded ammo fired fine but lost a couple hundred feet-per-second from published data. This powder had very little solvent smell and looked fine.

I was looking for a near max load.

I loaded rounds later in steps to see what I could wring out and did so just fine.

I would buy a new pound of Alliant Powder as soon as it is available and consider quickly using the older powder. 

I also loaded some rounds with a new can of IMR powder which had a potent solvent smell. These rounds followed published data very well. 

New powders often have a solvent Acetone like smell and over time the opened can will lose the solvent smell. Over longer periods, it will degrade to an acidic off smell.  When powder has that off smell it is time to dispose of the powder. Below is what Alliant says about storage and handling of modern powder.

https://www.alliantpowder.com/getting_started/safety/storage_handling.aspx

Another article I liked below.

https://www.rifleshootermag.com/editorial/how-to-determine-gunpowder-shelf-life/83922

Good Shooting!