You almost had a good formula in 2019 almost. Good hindsight would be, "maybe, after placing an order on our site, we don't make them travel to SDCC just to confirm an order they've already placed and just make sure everyone that ordered before the show gets a set in October. I mean, they clearly wanted what they ordered but since we didn't tell them what the exclusive was until well after the show sold out and people would have to scramble to get arrangements made to even get in the door to ge to our booth, maybe we could do better."
What you all did, in hindsight, was just produce an apparently small number of sets, make the ordering process a jumbled mess using a new market system no one was familiar with. Give no clear instruction on how to use it and set the number of sets per purchase at a point that cleared your inventory three times too fast.
So, yeah, your [as a company] hindsight ain't worth much. Sorry that you're the voice taking the flak but them's the job, right?
Here's a suggestion, as soon as you decide on what it is you want to promote at SDCC, post images of the set. Build a little hype for it and get people excited. A month or even six weeks before the show, take orders. Then, in October, ship out the orders to people who placed them.
If you really want to add a perk for those actually traveling to SDCC, which is insane to me because convention exclusives only alienate the majority of the fanbase who can't attend, maybe offer a small discount to those who show up at your booth.
Another idea is just do away with a Convention exclusive altogether. The inherent flaw with all exclusives is that SDCC tickets go on sale in what, August of the year before? And they sell out stupidly fast. Most people either know they are going or accept that they are not. Many months later and, usually, less than a month before the show, all these companies come out with their exclusives.
As a result, people wind up having very few means of obtaining them short of fighting over the scraps leftover or buying on the heavily exploited aftermarket. All of which creates a false demand for products and often hurts those that are collecting to actually want to own something.
--You know, I actually thought, "huh, with the convention not happening, maybe we'll all get a chance to own whatever is sold at a fair price." In hindsight, I wa horribly wrong.--
You can, instead offer, some sorta Mattel/Mega[dot]com direct to customer sets that we can, again, place preorders for over a set period of time and months later receive. You get your orders in and no one misses out. If you have a set number you need to make to make it profitable, produce those extra sets and sell them on your site of choice as a last chance before they are gone forever.
I know, there are bound to be some behind the scenes details that will need to be worked out to make this idea work but I don't think it is impossible. As I keep saying, that Battle Bones set was almost there anyway in regard to a made to order concept. The only flub in that plan was the mandatory attendance to SDCC. Eliminate that one step and you'll be that much better off.