Limited Collectors' Edition would, retroactively, begin with the 1972 issue of Rudolph, the Red Nosed Reindeer, although when the issue came out, it bore no such indication. These were all huge, oversized books. Most of them consist of reprints, although I believe the Rudolph ones have all new material. Because this series comprises new and reprint stuff, I am going to cover it the way I have done with DC Special and Super DC Giant.
The first Rudolph issue would later be coded C-20, and the later ones, one a year, were C-24, C-33, C-42, C-50 and C-53. Beginning a run with an issue numbered 20 is weird. The C likely stood for "Collectors'," from the title of the run.
I did read somewhere a theory on how the numbering came about. As I mentioned, the first Rudolph issue had no numbering, so it was the next one that launched under C-21. The theory goes that this book was considered the second volume of something. Perhaps DC Special. Maybe Super DC Giant, which had also been number with letters (S-whatever).
So the 2 at the beginning was not a signifier of 20s, but of volume 2. Thus, the first Rudolph issue, C-20, is really to be read Collectors, volume 2, number 0.
It's an odd theory, but better than any other reasoning I can come up with for starting a book at issue 20.
I've pretty much run out of things to say about the Rudolph books. Good thing I'm almost at the end.
The last Rudolph issue, C- 60, was released in 1978, but in the summer, and featured the character during his down time, rather than at Christmas.