That is a good question. The only one I know that has for sure acidified their apple sauce and apple butter is Ball and they found that the Fuji apples they purchased in the store were lower in acid so decided to add lemon juice.  I checked the National Center and their apple butter recipe is the same one they have had on their site for years.  It is the same recipe that was in the 2006 edition of So Easy to Preserve and uses a lot of vinegar as well as cider.  Their reduced sugar recipe only has cider and no vinegar.  Some of their fruit butters have lemon juice and some have orange juice plus rind added. I think that is more for flavor than for safety.  

The only butter recipe that I am aware of that is not recommended for canning is pumpkin butter.  It is made from a low acid food and could pose a botulism risk. 

As I said before, it is low risk to make apple butter from freshly picked apples.  The problem could be with Fuji apples that are over ripe and have been in storage.  The average pH of apples that are freshly picked is 4.0 and many are lower.  

Glad you are using up-to-date recipes.  If anything changes nationally, we will be sure to up-date our publications.  We are up-dating many of them so keep watching.  

Thanks for using Ask Extension

Nellie Oehler