I read this thread with some interest as I have 10x 250g “boxes” of SG stashed away. The oldest boxes are from 2012. I hadn’t really planed to cellar the tobacco in the boxes, it just worked out that way due to a number of things in life that took precedence and the fact I smoke fewer bowls these days and have way more tobacco than I can get to. I decided to open a 9 year old 250g SG FVF and report on what I found. Soon as I broke open the outer cellophane I could smell the tobacco and it was a deep rich aged Virginia aroma. The inner plastic bag was intact and sealed. The flake is dark, almost a solid dark brown. It IS definitely on the dry side, but not dried out. I prefer it on the dry side for smoking and it was near to what I aim for before loading up a pipe. I used a food processor I have modified to shred the entire 250g and the tobacco had enough moisture to come out perfectly the way I prefer. Lastly, I put it all in glass jars to stabilize the moisture content.
Bottom line is in my experience with the SG 250g boxes is that a few years in factory packaging is likely ok, but I would definitely recommend transferring any tobacco that you will not get to in 3-4 years to something more appropriate for longer term storage.
Cheers,
Ray