It's a reference to domestic vs. international market, nothing to do with the manufacturing date. Canon products sold (officially) in North America have a warranty which applies only in Norh America (nominally, anyway, since Canon usually honors the warranty for grey market items with proof of purchase).
That means North America vs. other regions will have different stock numbers (and different warranty cards, too).
Manufacturing data for some lenses used to be determinable from the date code stamped/printed near the lens mount, but Canon has stopped putting date codes on lenses, it seems.
