The selling dealer got that copy you have, and allowed the customer to have it.
It didn't come from within a hidden spot inside the car.
They (dealer) supposedly got body sheet / chassis sheet / car shipping record / and full Buildsheet copy.
Why anyone - or only very few got any or all of this stuff with their car - idunno
But it wasn't at all common practice.
Maybe some were good good buddies with the sales manager.
All of these are 1971 Norwood documents.
But i feel certain all existed for 1970 as well.
And complete Buildsheets like we see from Van Nuys cars
Your 70 Sheet is the only 70 Norwood i have ever seen.
These 71 sheets are the only 71 Norwood examples i have ever seen.
The only two 1973 Norwood Buildsheets i have seen did not come from within the car. They were furnished by the dealer to the customer. In one case, the dealer was the customer (73SD Black Primer Car).
I don't know why some 72 Norwoods had a hidden Bsheet, but no 70, 71 or 73 had them.
Too strange to do anything beyond accepting it as it is.