Given grees track record for screwing even simple things up do you really think something as potentially complicated as this would work. Also if up till now gree did not tag units with an in service date how would they back date older non tagged units.
In fact the more I think of it the more I would bet that units may not be tagged with a creation date other then the one when first designed by the artist so imaging how messed up it will be when units like valor units disappear the second you drop them in inventory.
Please please please put a fork in this idea before some greenius actually tries to impliment it.