How many Dell dual back-cover variants exist?

In the Overstreet Price Guide (41^st Edition, pg. 590) in FOUR COLOR listing there is a short note that says:

Issues beginning with #710? Were printed with and without ads on back cover.

When I saw this, I wondered:

Is it only the Four Color Comics that were published with and without ads on back cover?

Were all of the issues following #710 published with and without ads on back cover?

Over the past few years, I have catalogued over 95% of the Dell comics that have been published, or at least I thought I had.  When I catalogued the comics, I noted which issues had an ad on the back cover, and which did not.  When I was done, I asked Doug Sulipa if he could check his vast (and I mean VAST) inventory of Dell comics to determine which Dell comics had and did not have ads on the back cover.  It was a long process for him, but at the end, he found over 300 Dell comics that included both ads and no-ads on the back cover.  When added to the list I had catalogued, there were 331 issues that were located that were published with and without ads on the back cover.  I will refer to these issues as dual back-cover variants.

As I had suspected, the occurrence of dual back-cover variants extended beyond the Four Color comics.  To date, there are 61 titles that have been located with and without ads on the back cover.  Below is a listing with the counts by title (Note: DG = Dell Giant, MC = Movie Classics).

Title	Count
77 Sunset Strip	1
Bat Masterson	3
Ben Bowie	1
Ben Casey	1
Chip 'N' Dale	1
Colt .45	1
Dell Giant	9
DG - Bugs Bunny's Trick 'N' Treat Halloween Fun	1
DG - Bugs Bunny's Vacation Funnies	1
DG - Disneyland Birthday Party	1
DG - Donald Duck Beach Party	2
DG - Huey, Dewey and Louie Back to School	1
DG - M.G.M.'s Tom and Jerry Back to School	1
DG - M.G.M.'s Tom and Jerry Summer Fun	1
DG - Marge's Little Lulu and Tubby at Summer Camp	1
DG - Marge's Lulu and Tubby Halloween Fun	2
DG - Marge's Tubby and his Clubhouse Pals	1
DG - Mickey Mouse Summer Fun	1
DG - Moses and the Ten Commandments	1
DG - Picnic Party	1
DG - Uncle Scrooge Goes to Disneyland	1
DG - Western Roundup	1
DG - Woody Woodpecker's Back to School	1
DG - Woody Woodpecker's County Fair	1
Donald Duck	2
Dr. Kildare	1
Felix The Cat - Series 2	1
Follow The Sun	1
Four Color Comics - Series 2	219
Fritzi Ritz	1
Have Gun, Will Travel	3
Huckleberry Hound	5
Jace Pearson of the Texas Rangers	2
Jungle Jim	1
King Leonardo	1
King of the Royal Mounted	1
Lassie	1
Laurel And Hardy	1
Lawman	2
Looney Tunes	1
Ludwing Von Drake	4
M.G.M.'s Spike and Tyke	2
Maverick	7
MC - Jack the Giant-Killer	1
MC - Six Black Horses	1
MC - Tales of Terror	1
MC - Three Stooges Meet Hercules, The	1
Mickey Mouse	3
Millie The Lovable Monster	1
National Velvet	1
New Terrytoons	2
Peanuts	3
Quick Draw McGraw	2
Rifleman	3
Ruff and Reddy	5
Sea Hunt	5
Thirteen	2
Three Stooges	2
Voyage to the Deep	1
Walt Disney Presents	4
Wyatt Earp	1
Grand Total	331

The Overstreet Price Guide reference to Four Color #710 is the earliest dual back-cover variant for that series (Jul 56).  To date, I have located six earlier issues that include dual back-cover variant that precede that issue:

Donald Duck		44	11/55
Mickey Mouse		45	12/55
Donald Duck		45	01/56
Mickey Mouse		47	04/56
DG - Picnic Party		7	06/56
DG - Donald Duck Beach Party		3	07/56

The latest issues that I have located that include dual back-cover variants are from Feb 63 (Movie Classics – Tales of Terror #12-793-302, Thirteen #2).

My first question, regarding other titles, is clearly answered above.  However, the question regarding the continuity of the dual back-cover variants remains an open question.  Of the 614 Four Color Issues published between #710 and #1354 (accounting for the 31 issues that do not exist - or do they, see the earlier post on this topic), there are 219 issues that are confirmed as dual back-cover variants.  It is likely, but remains to be proven, that many of the remaining 395 issues are dual back-cover variants.  Expanding the search to include the other titles that also have dual back-cover variants, it is possible that there are hundreds of these variants remaining to be confirmed.

Locating these issues is a challenge.  Although eBay offerings will often include a scan of a comic’s cover, it is rare that they include a scan of the back cover as well.  When these do occur, it is possible to cross reference the issues against the list I have produced to date, but the process is extremely time-consuming.  Also, when looking for these issues at a comic convention or at a comic store that offers Dell back issues, the issues are usually boarded and the back cover is obscured.  This requires that each issue be removed from the plastic (or at least the flap needs to be freed) to determine the back cover’s content.  This is an equally time consuming task.

Possibly there are Dell comic collectors that are interested in adding to the list I have created.  If there are, please contact me and we can share data.