My Tresiba pens run out in about 15 days of daily use, but when on vacation I will take a spare pen. Usually, they are not stored in a refrigerator while I’m on vacation and there have been times when I’ve accidentally started using one shortly after opening the other. Putting all that together, I would say the oldest one I’ve ever used had probably been in use for no more than about 4 weeks with refrigeration about half that time. I’ve never noticed any decrease in strength. Not the range of experience you are looking for, but it’s all I can offer😊
The original thread was interesting to me. I only take one dose per day, but I do notice that it seems to tail off in the evenings (maybe 41 to 43 hours after the shot). I think this might be a reason for some people to take 2 shots per day. I use a higher Novolog dose per carb for my dinner and that seems to cover me pretty well.