The Brothers' War Retro Artifacts (BRR), including the schematic versions
BRO draft boosters correctly contain one (or sometimes two) BRR retro artifacts.
Packs always contain two Attractions.
For now, I've titled the extra versions of Attractions the same as I did with variants from Unstable: for instance, Balloon Stand, Balloon Stand (b), etc. I might decide to change this, depending on how deckbuilding sites like TappedOut decide to output the various versions, in order to make importing easier.
First of all, "Combine reprints" doesn't affect what cards are shown in the "All Cards" pane; it only affects how cards are added to your deck. With it checked, attempting to add a different print of a card already in your deck will instead add the print that's already there. The checkbox relevant to the full card list is "Ignoring doubles", and checking/unchecking that will change the number reported for "Shown" cards.
That said, you're correct that leaving "Ignoring doubles" unchecked still has a discrepancy of around 2,000 cards. The answer is... those are all the tokens in the plugin. You can view a list of all of them in the pane to the right of the play table (which can be shown by clicking the + in the upper corner if it's hidden). They're not shown in the deck builder since they can't be added to decks.
Fixed Hideaway scripts. New Hideaway cards should no longer erroneously ETB tapped.
Fixed Mechtitan Core so that it has a script to create its token
Removed the (nonplayable) Celebration cards. (I doubt anyone's been putting 1996 World Champion in their decks.)
Additional Unfinity spoilers
New cards (and some newly high-res images) for Secret Lair Drops, as usual
Some of the Pride Across the Multiverse cards (Bearscape, Collective Voyage, Heartbeat of Spring, Sol Ring, and Mana Confluence) were previewed by Wizards with incorrect collector numbers. Scryfall doesn't have actual high-res scans yet, but has updated their entries to match the numbers on the actually printed cards. You might have to delete these if you've previously downloaded them and they start appearing incorrectly for you in Lackey. (If you added this printing of Sol Ring to a deck, it will disappear, as its name has changed to reflect the correct collector number.)
I don't think WOTC is really forcing anything on anyone, except perhaps someone who was planning on playing any of these cards at a sanctioned tournament. So... probably no one. And I agree that some of them are probably reaching for it, but I don't blame them for wanting to rip a bigger bandaid off if they were already getting the most important one or two.
There are of course still plenty of images of the originals online, including on Scryfall. If I recall, I don't think I even deleted the Lackey-sized-and-cropped versions off my server. So yes, like turtlelemon said, if it's that important to you, you can change the ImageFile value back to what it was (which should be pretty clear from the cards before and after). If you've already played with them previously, Lackey will use your saved copies, and if not, it'll download them as usual.
A more permanent solution would be to rename and copy those original image files to the New Dawn folder where Lackey expects to find the replacements. That would persist across plugin updates.
P.S. Turtlelemon, you're a godsend for catching my mistakes, and SLD continues to be the bane of my existence. Uploaded the missing images.