Circumstances recently forced me to return to the UK to deal with the items in my long term storage. Amongst these I had about 5 ounces of Powerplant and White Widow which had been storing in glass or aluminium jars for just over 1.5 years. Last time I tried some was about 9 months ago and then it was INCREDIBLY STINKY and pretty damn strong. The trichomes looked cloudy (not amber) on both and the highs were pretty intense.
Now when I got the jars out this time I noticed the smell had greatly lessened. It used to be the case that if you opened a jar the whole house stunk of weed within 60 seconds, but now it was just a gentle waft of spicy aroma. The main difference though was that the trichs on mainly the white widow had turned completely brown! I thought it was mould or something at first, but a look under a loupe showed that almost all had turned from Clear/Cloudy to brown. It was definitely not like this last time I saw it. The Powerplant had a scattering of brownish trichs but it was mainly on the WW.
The smoke had become more trippy, crazily strong, but still not too couchlocky. The first time I really properly smoked it I had a full on panic-attack and near white out after hitting just a couple of bowls in my pipe

something I never do, especially after such a small amount. There was a greater alertness - like drinking 5 double espressos - and my muscles became kinda twitchy and tense. It was possible, though inadvisable, to go out in public after smoking, even if it did make your eyes into bloodshot dope-fiend identifiers. Seriously, it had developed full on tripping characteristics which simply weren't there before - a bit like light shrooms in the disorientation and balance departments. Not something that's too pleasant when you're expecting a nice chill and conversation.
The aroma when broken up was still rich and the flavour when smoking was stronger and more refined than last time. The flavour lingered in my mouth for much longer than before and was nice with a nice cold glass of water.
Conclusion from my little study - Weed is "best" between 3 months and 9 months cure, then can develop into a very different smoke. After 1 year I think aroma decreases and the THC either degrades into secondary cannabinoids, or converts to CBN. Either way, it makes it a more devestating smoke.
It was in fact TOO STRONG for me - so I only got through a little bit before packing it away in a different location for another year (or so). So one year from now I'll give you a smoke report again when it'll be 2.5 years old. Should be.... interesting.
B8 - doing it all in the name of science!