Differences between the same lens

This is a bit of an odd issue, so please bear with me and read carefully. Because I liked my 85mm 1.4D lens so much, I bought another one after about 4 years. The seller posted the serial number, so that prompted me to look up known serial numbers on photosynthesis.co.nz I learned that there were 3 separate productions of this lens beginning in 1995. The first "batch's" numbers went from 200*** to 228*** and was produced from 1995- (unknown). The second batch's number ran from 300*** to 303*** and all were produced in 2005. The third and last batch's number ran from 400***-469*** and was produced from 2006-2010. Here's what i'm saying: I have one of the lenses from the first batch produced (serial # 225*** US Version) and one of the lenses from the last batch produced (serial # 456*** Grey Market). I have noticed that the lens from the last production run is absolutely sharper, at least at larger apertures and definitely in the center, than the lens from the first production run. Although the older lens seems "warmer" and has more character somehow, it's hard to explain (I shoot portraits and street photography). I know this observation may seem irrelevant, but I guess i'm that 1% that looks at very subtle detail. In my equipment and when i'm editing photos. Is there anyone who can give some advice on this? I have even noticed differences between the same model camera. For instance, I have 2 D300's. And one of them focuses noticeably (and substantially) faster than the other. It hunts much less and attains accurate focus quicker. Thanks so much for your input!

i don't find this surprising. I even if this lens is the same design, the equipment used to assemble and or produce the parts has most likely changed. Even if two item come from the same production run the tolerance of individual items vary. So if two parts are fitted together and one is at the plus end of the scale and the other at the negative they will not fit the same as two that are at zero variation.