When I started typing this post, I didn't remember any dates. But while looking for a box which someone got empty and wanted to fill properly, I found some dates.
So anyway, yes, it was my thought that they all predate the mid-1950's or whenever it was that Marble King started making Rainbows. (Howdyshell in his interview in AMMM said they started veneering in 1956 or 1957.)
If I got one with Marble Kings in it, I wouldn't remove them. However, I would suspect they were backfilled. If a lot are found that way, my guess would be that this was because so few people have known what was supposed to go in them. I could see people changing the Pelts out because they just didn't know that Berry Pink was jobbering for Peltier when these boxes were made.
The 1953 ad I linked to above doesn't list them. AMMM shows a 1954 ad which looks like the 1953 ad. I think maybe I've seen a 1955 ad which looks roughly the same. Not sure where I would have that one. Probably a paper copy which I have stored in a box. Gotta index that box. It's the one filled with goodies from George.
Okay, next post will have some dated material showing the Champion version at least. Think I might also have something which says Marble King on it. Not sure. Gonna take a minute to look. Be right back.