if Nikon only uses the G1 lens formula and have to grind their own lens elements then it is essentially them utilizing their own resources to build someone else's lens, which defeats the whole purpose of the outsourcing
Not to be argumentative but some situations it'd make sense:
1) they outsource the lens grinding, but either can use a patented coating of their own that the original maker couldn't, or use a publicly-available one that's better but more expensive
2) they in effect outsource the formula design stage, which might make sense if they have manufacturing capability but their designers are busy. (Car companies often outsource parts of their design work to firms like Lotus, for instance. Or the opposite: the main company does the design then outsource production, as Porsche did with the Boxster. Or, as with BMW and the X3, outsource both design and production, to by Puch in Austria, while Puch of course could use BMW patents and trademarks such as the Hofmeister kink, and the final product is badged and sold as a BMW. Or, as with Diamond Star, one company (Chrysler) specs a car it would like to buy from another company (Mitsubishi) which does the actual design and manufacture, then they both sell it. Chrysler certainly had the ability to design and manufacture cars, but for surely good business reasons saw an appeal in another firm doing that while Chrysler concentrated on sales.
3) maybe Nikon did the original design and licensed it to Tamron to use as their own product?
In general, a company's not going to have a perfectly-balanced workflow with all departments equally utilized:
-- basic research
-- design of optic formula
-- construction
-- sales
so it makes total sense for Nikon, OR Tamon, to outsource a stage they're already saturated on, whichever stage that is.
