Most sites and stores have given up on listing the Mystery Booster promos separately from The List, and merged them together since it seems most of the time it is impossible to distinguish between them (although it is claimed for some the plainswalker symbol is a slightly different size).
I have also done the same on deckbox now, and moved all of the "components" in "The List":
- Mystery Booster
- Mystery Booster Retail Edition Foils
- Heads I Win, Tails You Lose
- Angels: They're Just Like Us but Cooler and with Wings
- From Cute to Brute
The edition listing is split by the edition symbol on the card, with collector numbers corrected now so that they show what is on the card.
Predictably, the page is now very laggy for editing individual lines of it via the checklist buttons on counts, since there are 3400 rows with a lot of dynamic controls on each. I will take a look at optimizing javascript initialization and performance on it if it stays like this. Another option would be to make it more readable and manageable by splitting it into small editions, one for each edition represented "The List - Kaladesh", "The List - Ixalan" etc. I didn't decide yet how to proceed.
Some printings were duplicated, and they were merged now automatically, if you had them in your collection nothing should have changed except the printing will be "The List" instead of "Mystery Booster", or whatever it was before.
I updated the CSV importer code finally to also only look at the "Printing Id" field for identifying printings, so that changes / fixes of edition names, card names or collector numbers in the database cannot break the import of some rows in collections exported to CSV.