Uncle Scrooge No. 49 to No. 53 and No. 55 to No. 60 only have the title mentioned, though a penciled alternate cover version for "The Swamp of No Return" (US 57) contains the text:
I DON'T REMEMBER ME!
Goldkey reprints of Uncle Scrooge No. 63 and No. 65 have the same texts as the original, but arranged differently. Issue 67 - which contained a reprint - hasn't got a promotional text on cover. So, maybe this could indicate that the texts were Barks' idea. But even if so, maybe some of them were too weird for his editors, which may explain why there's suddenly the simple line "exciting adventure" on Uncle Scrooge No. 68.
Another exception could be "House of Haunts" (US 63), for which Barks originally had the title "His Shining Hour", but was changed by the editors. Reading through Barks' notes shows that the story was submitted to the editors on August 3, 1965, while the cover was submitted on September 12, 1965. So, maybe this means that Barks knew about the title change in advance?
Also, it seems that after Barks' last story, "King Scrooge the First" (US 71), a couple of (Strobl) issues lacked the promotional texts. At some stage the editors got this up and running again. So, if Barks had no hand in the promotional texts, this would be a very clear example of coincidence in general.