Its a really good idea to date all mixes and jot down the recipe. If it sucks at anything over 6 weeks it is very likely trash with maybe the exception of tobacco flavors.
If I still don't like something after a deep steep (too strong), I'll cut it in half or quarter it with unflavored to see if that helps.
Often enough, steeping simply allows the flavor molecules to more evenly distribute throughout the liquid. In some cases like mints you can go as low as 0.5% and get a very nice fresh mint flavor, yet its often suggested to use far higher percentages.
A lot of what we see as bold flavor in premium e-liquids is not more flavor, but well steeped flavor.
I don't disagree with anything you are saying, I just don't think it's the best way to mix, particularly for new DIY'ers. I have been lucky enough to work with some of the top juice makers in the country, and if there is one thing I can share that they all universally agree on, it's this:
"If it's not good at the time of mix, it'll never become a great juice."
Most of you would know some of these brands and their makers. I was quite surprised to hear this myself, because I had believed this long-steep time non-sense myself, once upon a time. Long steep times will always change the flavoring of juice, or practically anything else, for that matter. The problem is that it rarely results in great juice, though, sometimes it does. And because it sometimes does, some juice makers think this IS THE WAY to do it, and it's not, in my opinion. So, while I agree with what you are saying, it's not the best way to learn to make juice.
I've tried for many months to help show new DIY'ers on this thread how to learn to make good juice, and we seem to have some good results, and some appreciative folks. So, I'm not saying you're wrong, because you're not, it's just another, more difficult way to do it. I just want all to be clear about this point. Making great juice does not require longer steep times, it requires either higher initial flavoring, which you can taste as "GOOD" right out of the can, and then adjust to suit taste, over and over until it is great, a process that takes me about 30 minutes, OR, you can take weeks of steep time and rarely make a good./great juice. This has been my experience, and like I have mentioned, I did lose about 6 months trying the long steep time method and ended up with only one good juice. In the next six month using a higher flavoring method I had 25 ADV's. A year later I had 150 ADV's. Never, ever could have done this with long steep times. Nor can you. Not 150 ADV's, my friend. No one can, it takes too long.
Ok, I've said my peace. Truly, no offense meant or intended. Just trying to give my actual experiences and keep it real here. You'll find me on this bandwagon hard and heavy about every three months. Good luck to you.