Determining the age of an EOS lens.

Can anyone advise me how I can find out the age (manufacturing date) of my following three lenses:-

EF 70-200 mm f/4L IS USM

EF-S 15-85 mm f/3.5-5.6 IS USM

EF-S 60 mm f/2.8 Macro USM

The reason why I am interested to know in which month/year they were produced is that we all know that manufacturing technology has made substantial progress in recent years resulting in improved quality compared to when these lenses were first announced.  Although all three lenses work well on both my 450D and the 60D, I am somewhat in doubt whether the reputable dealers have sold me some "old Stock" at full retail price.

When I approached Canon with my question I was given the respective "release dates" of these lenses (which did not help) and the reply was  that any information about lens manufacturing dates from Canon Europe was unobtainable.  I submitted the serial numbers of these three lenses, but it appears that no record of the manufacturing date is kept by Canon, which rather surprises me, nor does the excellent link "The Age of a Canon Lens" could give me any clue as to when my lenses were produced.

I suppose any other interested parties wishing to find out just when their recently purchased expensive lenses were produced, will have to remain a unsolved mystery, or am I wrong?

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