The problem was that the SNP document was a total work of fiction. They assumed England would simply pay Scotlands national debts, set up a favourable trade agreement, vote for them to be allowed back into Europe, and gift them all of the oil (which according to international convention is in English waters, not Scottish ones).
Then presumably, if the Vote Leave document were similar, it wouldn't have passed review.
(There still is no Vote Leave document. Not even the ERG can summon one up after all this time.)