To me the "26 volumes of the Warren Report" means the whole package, including the report itself, nut I'm more than happy to simply agree to disagree on that.
Selectively gathered evidence published in 26 volumes is also an expression of an opinion.
From Mary Ferrell Foundation website:
Warren Commission Hearings and Exhibits
The Warren Commission published 26 volumes of hearings and exhibits within a few months after issuing its report. Volumes 1 - 5 are hearings conducted by the Commission members in Washington DC. Volumes 6 - 15 are hearings conducted by staff attorneys on location in Dallas, New Orleans, and other places. Volume 15 also contains an index to names and exhibits. Volumes 16 - 26 contain photographed Commission Exhibits, usually abbreviated to CE (i.e., CE 399), plus other exhibits organized by name.
1. Warren Commission Hearings, Volume I
2. Warren Commission Hearings, Volume II
3. Warren Commission Hearings, Volume III
4. Warren Commission Hearings, Volume IV
5. Warren Commission Hearings, Volume V
6. Warren Commission Hearings, Volume VI
7. Warren Commission Hearings, Volume VII
8. Warren Commission Hearings, Volume VIII
9. Warren Commission Hearings, Volume IX
10. Warren Commission Hearings, Volume X
11. Warren Commission Hearings, Volume XI
12. Warren Commission Hearings, Volume XII
13. Warren Commission Hearings, Volume XIII
14. Warren Commission Hearings, Volume XIV
15. Warren Commission Hearings, Volume XV
16. Warren Commission Hearings, Volume XVI
17. Warren Commission Hearings Volume XVII
18. Warren Commission Hearings, Volume XVIII
19. Warren Commission Hearings, Volume XIX
20. Warren Commission Hearings, Volume XX
21. Warren Commission Hearings, Volume XXI
22. Warren Commission Hearings, Volume XXII
23. Warren Commission Hearings, Volume XXIII
24. Warren Commission Hearings, Volume XXIV
25. Warren Commission Hearings, Volume XXV
26. Warren Commission Hearings, Volume XXVI