Every cocoa powder, unless it's lecithinated, will have the same shelf life if properly stored. Assume proper storage conditions, and it's not lecithinated, your cocoa powder will be good for up to three years.
Can you tell me what you mean by "unless it's been lecithinated"?
And why am I always reading that cocoa powders with a high fat content have a low shelf life?
A very small amount of cocoa powder will have been processed to contain lecithin. Unless you've specifically asked for it, yours is not.
Why do you read that? i've no idea 8) i've read lots of crazy things on the internet.
One t hing you'll need to watch with higher fat powders is that they will be more susceptible to both temperature and pressure, in that the fat in them may melt or squeeze out, and when it resolidifies, will turn yoru bag of nice powder into a brick of solid cocoa. however, it's still fine, it's just needs to be reground.