The DND 419 is a document that DND never intended to be used as a proof of citizenship. They only issued it for a limited period of time. They only used that document between 1963 and 1979. It doesn't cover the whole period of the 1947 act.
The provision in Bill C-37, in proposed paragraph 3(1)(g), is intended to resolve the problem of the 419 and the confusion that had arisen as a result. If Bill C-37 is passed, the distinction between a 419 and a registration of birth abroad will be eliminated.