LBF is one of my daily smokes.
Fresh LBF is a little rough on the palate.
1 year old LBF is smoother, but not as complex.
2 year old LBF is smoother, sweeter and just starts to develop a deeper complexity to the smoke.
3 years brings LBF to what I think is the beginning of it's peak. Smooth, sweet and with just enough complexity to keep a bowl from getting boring.
Years 4 and 5 are much like year 3, but by year 5, I start to get some additional fermentation going in my jars that makes a tart ending to each puff.
After year 5, can't help you, I've never had any last that long.
What I started doing several years ago was to buy the 1.5lb boxes of LBF. Those usually last me about 3 months in my normal rotation. The first two years, I bought 4 boxes and bagged them in mylar. Then in year 3, as I smoke a box, I buy 2 to replace it. Only the last year or so have I not been able to replenish LBF like I normally do, but that has been due to the shortages of LBF on the market. So I suppose my response is much like Mr. Owl's on Tootsie Roll Pops. How many licks does it take to get to the center of a tootsie roll pop? The world may never know.