That changed in the 1970s, when George Olshevsky (owner of a set of Marvel Comics himself), put started a series of Marvel Index magazines, that contained that information in multiple volume form, focusing on a character or small group of characters in one particular magazine volume.
Here are the first two of those magazines, one focused on the Amazing Spider-Man, the second on Conan and the Barbarians.
The Amazing Spider-Man
...but, these, along with various Spider-Man centric titles were covered in this index.
The issues covered here are:
(Tales of monsters and alien invasions, including adventures of Dr. Droom, all by Stan Lee, Jack Kirby, Dick Ayers and Steve Ditko)
(Even more aliens, invasions and oddly named monsters....all by Stan Lee and Steve Ditko)
Amazing Fantasy #15 (August 1962)
(the issue that started it all, but was the last of a run)
(this is the majority focus of this index, featuring Peter Parker, Doctor Octopus, Green Goblin, Kingpin and oh so much more excitement and adventure in all those issues!)
(oversized issues, started off with big new tales including the premiere of the Sinister Six, later issues reprinted hard to find original stories from earlier issues)
(larger, magazine sized tales of Spider-Man, in continuity with the regular comics)
Amazing Spider-Man (Mini-Comic) February 1969
(Reprints Amazing Spider-Man #42, revealing the face of Mary Jane Watson!)
Giant-Size Super-Heroes #1 (June 1974)
(featuring a meeting of Morbius the Living Vampire and the Man-Wolf, both who got spin off series in Marvel monster titles)
(special team-ups of Spider-Man and other characters, including Dracula, Doc Savage, Master of Kung Fu, the Punisher and the Man-Thing, with a Spidey/Human Torch reprint in the last issue)
(stories published in conjunction with the Electric Company; simpler stories for younger readers, to get them interested in Marvel Comics, and not tied to the main continuity).
All of which had a black and white picture of the cover, title of the stories, writer and artists, main first appearances and comments.
A separate section in the back had a cross-index of Spider-Man comics by personnel, and another cross-index by appearances of characters.
Conan and the Barbarians
This issue also features bits on King Kull and Solomon Kane, a little taste of Red Sonja, Sinbad, Thongor and Gullivar Jones (all licensed by Marvel at the time) as well as Marvel characters Ka-Zar, Shanna and Man-Wolf!
The issues covered here are:
(Tales of Conan, including the premieres of Thoth-Amon, Red Sonja and adaptations of stories by Robert E. Howard and Gardner Fox, and monsters and sorcerors galore)
(Early Conan reprints)
Giant-Size Conan #1-5 (September 1974 to 1975)
(Some new stories, some reprints, and some a mix of both)
(Magazine sized black and white stories of Conan, and others like Red Sonja, King Kull and Blackmark, not under the Comics Code Authority)
(Reprints of Conan the Barbarian stories, a story from Monsters On The Prowl and one King Kull tale with a cover painting by Enrique Badia Romero)
(reprints of Ka-Zar/Lord Kevin Plunder appearances with his pet sabretooth Zabu in X-Men, Amazing Spider-Man and Daredevil, with new Hercules and Angel stories in the back)
(skipping Ka-Zar's appearances in Marvel Super-Heroes and Astonishing Tales, issues with new adventures of the hero of the Savage Land, including Shanna, Zabu, Klaw and more)
(King Kull of Valusia is another creation of Robert E. Howard, set in a time 8000 years before Conan, who premiered in Creatures On The Loose #10, got his own title for two issues, had the story finished in Monsters In the Prowl, then had his own title revived with issue #3, facing monsters including Serpent People)
(Kull's title changed from the Conqueror to the Destroyer, as his foe, Thulsa Doom, took control of Valusia, and this story continued in...)
(With a first issue full of reprints, Kull's saga continued in the next two issues of this black and white magazine, along with stories of Red Sonja and Solomon Kane - another creation of Howard's)
(Starting with tales of Conan, as well as the Femizons, as well as the premiere of Man-Thing, this black and white magazine switched over to tales of Ka-Zar, Shanna the She-Devil and Brak the Barbarian)
(Reprints of Astonishing Tales of Ka-Zar and Zabu, with some art by Barry Windsor-Smith before he worked on Conan)
(Though only the first two issues are indexed, due to having stories with The Dragon Slayer and Brak The Barbarian, covers for all 21 issues are included in the index)
(Only indexing issue 4 with Starr the Slayer, it does feature the 8 issues of this horror title)
Chamber Of Darkness Special #1 (January 1972)
(The one and only special for Chamber of Darkness cover in the index)
(Continuing numbering from Chamber of Darkness, reprints of monster tales from before Fantastic Four #1, including stories of Xemu the Titan, originally called the Hulk in Strange Tales, and It the Living Colossus from Tales Of Suspense, along with a few new King Kull tales)
(A few fighters, like Beowulf, Vandal the Barbarian and King Hamand, plus horror reprints)
King-Size Tower Of Shadows #1 (December 1971)
(One special, cover only)
(Switching over from Tower Of Shadows, first, horror reprints with King Kull for a few issues, then the title changed...
(Odd novel and movie adaptions, switching to movies with the Golden Voyage of Sinbad)
Fantastic Four and the X-Men, but those are tales for the future!