While surfing the web to find out how much vitamin A and vitamin D is in cod liver oil I found the following.
Various companies selling cod liver oil have found that there is too much variation in the amount of vitamin A and vitamin D in the natural oil.
So, they remove all of the vitamin A and vitamin D and then put in the amount the the govt says should be in there.
Unfortunately it still appears that the ratio of vitamin A to vitamin D is often too big.
See many files on this wiki for details.
Sorry I do not have detailed references.
Busy on too many other vitamin D topics just now.
Perhaps someone else could fill in the details - at least by providing comments at the bottom of this page