This is a subsidiary post of Editorial Activity of the New Testament.
This link to Vulgate shows that Paul was named in the title to Hebrews.
Note the similarity of form in the titles, which implies an editor’s hand:
Gospel “The gospel according to…”
Letters of Paul “To the…”
General letters “[number] [name]”
How far back do these titles go in the mss evidence?
Metzger, Bruce M. The Canon of the New Testament: Its Origin, Development, and Significance. Oxford University Press, 1987. See “Appendix III – Title of the Books of the New Testament” beginning on p. 301.