UniBond 800 does appear to have shelf life issues that were not as common with URAC 185. I was told long ago to keep it in the freezer and have only had the problem once since then - - - which was the time I left it in the garage instead of putting it back into the freezer right away. Heat does most certainly ramp up the rate of reaction for Unibond 800, once it kicks over, it is off to the races...
I would suggest buying it directly from Nelson and even asking them for a batch run date to be written on the can label. I think mine had a stamped on date for the last I got from them. I like the results of Unibond a little better than for Smooth-on, but opening a NEW CAN of expensive but dead glue will move the needle on your opinion meter rather dramatically. I use it for other wood working projects as well as bow building, or I might have left them already.
OneBow