This article is from the Stardates in Star Trek FAQ, by Andrew Main zefram@dcs.warwick.ac.uk with numerous contributions by others.
Objection: in the ST:TOS episode "Journey to Babel", SD [19]3842.3
(2268-02-26), Sarek states that he is 102.437 years old. In "Sarek", SD
[21]43917.400000 (2366-12-01), he is said to be 202 years old. That is an age
difference of 100 years, but the episodes took place 98 years apart.
It is possible -- in fact, very likely -- that these are references to Vulcan,
not Terran, years. As it is entirely possible that only one (most likely the
second) age reference is in Vulcan years, it is not possible to reliably
determine the length of the Vulcan year from these data.
There is another possibility. As the discrepancy is only two years in a
hundred, it is conceivable that one or both references were to Sarek's
subjective age, with the discrepancy accounted for by relativistic effects.
 
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