You're mis-reading. The first 6 *787s* are not up to par, to the point of airlines not wanting them. Most airliners are to full-spec from the very first one. First 777 ever built currently flies for Cathay Pacific. First MD-11 is with FedEx.
Actually, the Concorde has an above-average number of prototypes and pre-production examples (those are 2 different things when talking about the Concorde) and percentage-wise has an insanely-high number of "not delivered to the airlines" examples built.
Also, static-test airframes are never counted in any category/total, they aren't even assigned line numbers and don't count as part of the production run. (especially since they're never finished, sometimes never getting past the 55% mark or so)