Back when Nintendo Power magazine
was a bimonthly publication, the editors at the magazine decided to publish special guides in the off-months that, unlike the NP magazine which covered a few levels of many games, would cover one game from beginning to end. These guides would be sent as part of the subscription price to Nintendo Power
subscribers and were called the Nintendo Power Strategy Guides
The first guide, a complete walkthrough of Super Mario Brothers 3, was released in June 1990. Others followed every other month. However, when Nintendo Power went monthly in January of 1991 the guides ceased publication and gave way to the Nintendo Player's Guides.
The complete list of Strategy Guides:
The guides are long out of print and used to be available as Nintendo Power
back issues when the magazine was bimonthly. By 1992 they were gone from retail channels forever, relegated to used game shops and online auctions. Nintendo
: Now You're Playing With Power!
I used to have all these guides. I still have the SMB3 one for old time's sake.