Well, I too would recommend "Apples for the 21st Century", and I saw copies for sale at Portland Nursery last Fall.

Moreover, copies can usually be obtained either on E-Bay, or the ABE Advanced Book Exchange.  I once bought one, for less than 10 bucks, with free shipping.

I'm also fond of "Fruits for the Home Garden", by Hedrick.   A Dover book.  Usually paperback.  But, hard to find used.

Those vague statements in catalogs, are derived from such books as the above.

There just aren't that many great books on the subject.  Few people have grown and tasted, the myriads of obscure fruit varieties listed in catalogs.   So, sellers rely on quoting "experts".  Some, from long-bygone eras.

Heh, heh...  In fact, Manhart, a guy many of us knew, has become one of those immortal "experts".  I see him quoted, as if he were Moses.   And, that is how it goes.  A few guys, a few great books.  And, not too many living people, who have actually tasted all of the exotic fruits in question.

Good timing for those of you wanting a copy of Manhart's book.  Lot's of copies available, at bargain prices.  A Deal!

https://www.abebooks.com/9780486229447/Fruits-Home-Garden-Hedrick-0486229440/plp

https://www.abebooks.com/servlet/SearchResults?isbn=0964841703&cm_sp=mbc-_-ISBN-_-all