Its always been the same with Vettes - 'new' marques or the car in initial production stages seem to either 'use-up' existing stocks of components that are either 'on the shelf' or (as you 'intimate') commited from sub-contractors for contractural reasons.
As a 'new' buyer, arguably there is a perhaps degree of comfort for buyers weary of being the first users (and test guinea-pigs) for newly introduced tech.
My '68 despite a totally different body and interior to the vastly different looking C2 forerunner has much of it mechanical side carried-over from the '67 big block.......hence effectively being a one year only variant. So engine, transmission and ancillary engine components are as per '67 - even the radiator and its hoses are '67 carry over, despite the radial change in front-end proifile. Other items (like front grille mounting brackets) seemed to be almost hand fabricated.
I think that due to the significant differences in body structure and related components like side windows and removeable rear windows and other seemingly one year only parts a lot of the differences were due to GM effectively learning 'on the job' and really it shows they were way behind in offering a finalised product ready for series production for 1968. Fortunately the 'hands-on' type of production required on the Corvette production line would have (and presumably still is) ideal for making running changes quicker......unlike perhaps regular 'shoe-box' type of vehicles.
Pre C8 GM would do contracts with tier 2 suppliers for cheapest costs for GM
Thus meant more out-of-pocket money for GM plus all the costs for inventory, bookkeeping of it, etc
So reason lots of older gen went into next gen
With the new parts' policy, no inventory meant the C8 has very few parts of a C7
Now so bad is GM requires suppliers to daily supply parts to BGP for the amount of C8s built for that day
This is a big negative as now not having pats inventory you see with the C8 many times C8s cannot be completed
as lacking of parts not on hand.