I saw this archival image of LEGO owner Kjeld Kirk Kristiansen playing with LEGO at about age 2-3 in the Billund product display room that dates to circa 1950-51. I looked at the Automatic Binding Bricks that little Kjeld was playing with and saw something odd...

OK... a little background first (since most of you are not familiar with the Automatic Binding Bricks early LEGO of 1949-53)...
Here's the similar box designs of the 700/1 (large), 700/2 (medium) and 700/3 (small) first LEGO sets under the Automatic Binding Bricks name starting in 1949....

Well TLG was going to produced some smaller sets called 700/4 and 700/5... and they sent out a "New Items Info Sheet"
to their Danish LEGO shop owners...

There was only one problem.... while the larger 700/1, 700/2 and 700/3 sets are in circulation (and worth quite a bit on the secondary market).... for some odd reason there are NO KNOWN examples of these 700/4 and 700/5 smaller sets in any private collection.
In fact, the earliest known 700/4 and 700/5 sets are of the LEGO Mursten design that came out later in 1953.... with Kjeld and his older sister Gunhild on the box top...

Getting back to the earlier unknown version... 2 years ago I asked the folks at the LEGO Archives/Collections if they had either the 700/4 or 700/5 Automatic Binding Bricks boxes in their collections. They told me that they have no real info on those 2 early sets, but that they did have an example of the smaller 700/5 set in the Billund Collections... and here's an image from them...

They could not locate an example of the larger 700/4, and weren't sure why no one has an example on the secondary market. (LEGO Archival info from the early days tends to be rather sparse.)
Well I posted that picture of a 2-3 year old Kjeld on Facebook a few weeks ago... because upon closer inspection, he was playing with a 700/4 set (I can tell from the box content configuration that it was that larger of the 2 sets).
Well after I posted that Kjeld image on Facebook, one of my German LEGO acquaintances was going to some LEGO gathering where Kjeld Kristiansen would be at.... and he took a copy of that early image of Kjeld playing with the still unknown early 1950s 700/4 set with him to the event, and personally asked Kjeld about that image and the boxed set. Kjeld's comment to my LEGO acquaintance once he saw the photo.... "oh yeah... I was playing with one of the Automatic Binding Bricks sets that were never put into production"! :-O
So in one sentence Kjeld said something that the Archives were mum about... and which kind of stunned me!!!
The above colorful 700/5 set was just a prototype mockup boxed set that was never placed into production... and the now missing larger 700/4 prototype mockup box..... well someone wanted to take a photo of Kjeld playing with Automatic Binding Bricks... and they just grabbed the prototype 700/4 set... let him build with it for the photograph... and the box either just got tossed away, or it was sent home to someone as used LEGO.... and is probably gone forever... in the dustbin (trash) of LEGO history!! :-O :-O :-O
It's the Sherlock Holmes sleuthing like this that makes researching LEGO so much fun for me... :-) I just wish the outcomes weren't always this painful! :-(
Comments
As soon as I saw the title in my feed I knew this was going to be a good story from @Istokg. Fascinating! It's great that your German friend was able to ask Kjeld personally.
There could also be some more recent sets that might have never made it to production. At least that's what I'm thinking when I see LEGO skipping numbers in a series of sets. Maybe there is a prototype somewhere at LEGO's HQ that never made it to production, but we might catch a young Kristiansen child playing with in some random picture. :)
(Although, if you send the prototype home with the talent, I suppose you can't expect it to be returned...)
However what fascinates me most about this photo are the toys in the background. On the left you have a Farmall tractor on the top shelf and a large Chevy on the bottom. I'm not family with the trailer the Chevy has. It looks to be all plastic, but the size is highly unusual. The Farmall tractor is quite rare compared to the Ferguson tractor. I'm still actively looking for one.
On the other side working top to bottom and left to right, you have some early trucks (30s or early 40s) and more modern truck (late 40s or 50s) all with milk cans, some farm sets, another truck with a trailer, that weird pull toy with round block of wood the rotates and a bucket. The farm sets are really interesting. The one on the right looks to have figures and animals.
As for the 700/4 and 700/5 Automatic Binding Bricks sets... although they were never put into production as Automatic Binding Bricks sets.... besides sending out a faux announcement to Danish retailers... TLG also sent out a faux announcemnt to LEGO customers in their 1951-52 Automatic Binding Brick Catalog.... something that they've done a lot in the 1950s and 1960s.... (and even later!).
This is 2 of the 8 panels of the Danish 1951-52 Automatic Binding Bricks 2 sided (4 panels each side) ABB catalog. And it mentions both 700/4 and 700/5 sets, even they weren't produced until LEGO Mursten sets came out in new boxes in 1953.
This is a repeating problem for LEGO catalogs for many years. It seems that the LEGO Archives folks and the LEGO Catalog folks at TLG mentioned the new sets... even before the decision to release the new sets was cancelled.
More LEGO Mayhem!