At first I didn't think I would have enough, then I did a massive brainstorm of possibilities and started crossing off some that didn't have runs I loved enough to include and started formulating an initial draft of 12. Then I had a second wave of inspiration that produced another 12-15 candidates, many of which made their way into my final 12 leading to some that were in my initial 12 to be cut. Then I spent a couple of days puttering with that list sliding things in or out, made a "final version" then did one last revision of that just as the entries started (swapping out my day 2 entry I believe). So there were a fair number of characters who got consideration through the process.

Some of my near misses included:

-Wolverine-he was on my list but ditched late (just as I was writing up my pieces to post on the eve of the first day) to make room for Zatanna

-The Authority-they were one of my last cuts to get to 12

-Son of Satan-he debuted in the pages of Ghost Rider and then into his Spotlight and solo runs. He survived the first few cuts but didn't make any version of my final 12

-Robin-both Dick Grayson and Tim Drake got consideration, and Nightwing was in my first draft of the 12, but was replaced when I had a second wave of ideas that included 3 that made my final list

-Barks' Uncle Scrooge, but I decided to limit each character to only 1 entry on my list and went with the Rosa run, but I had both versions of Scrooge in my initial draft of the 12

-Same with Black Panther, the Kirby and McGregor runs got consideration but I went with the Priest run when I made my first draft of the 12 that included Panther

-The Kendra Saunders version of Hawkgirl started as a supporting character in JSA but eventually took over the lead from Hawkman in his book and it was retitled Hawkgirl, but I am not sure if that would have been eligible.

-Chase-Cameron Chase 1st appeared in Batman #550 before getting her own short-lived series that I absolutely adore, but it was one of those murky appearance to set up and promote the new series so I wasn't 100% sure it was going to be eligible and I had other stuff I wanted to spotlight

-wasn't sure if Dreadstar could be considered a spin-off of Metamorphosis Odyssey since Vanth wasn't the main character in the first couple of installments of MO, but that one felt iffy, so I didn't use it

-Warlock spinning out of FF and into the Starlin run was on an early list but didn't make the initial cuts

-briefly considered Cable, and was looking at the brief run by Ladronn, but there were so many characters I liked better it never got serious consideration

-thought about Scarlet Witch, but the solo series by James Robinson that was my favorite was from 2016 so not eligible

-Ka-Zar was on an initial brainstorm list but didn't make it past that stage

-thought briefly about the Walt Simonson Orion series as a spin off of New Gods but again didn't make it past that initial brainstorm list

-Mark Waid's Flash run featuring Wally West was on the list for a while, but got cut when I started trimming towards 12

-I wanted to give Guns of the Dragon another shout out, but wasn't sure if a team up/cross-over of existing characters (Bat Lash, Enemy Ace etc.) counted as a spin-off of those characters and I had a lot of other options, so I didn't pursue it past an initial hmmm phase.

-briefly thought about Merv Pumpkinhead from Sandman, but wasn't sure he ever got a 3 issue solo series, he had a one-shot and an arc in the Dreaming as a protagonist but wasn't sure that was enough

-Constantine was another on my initial brainstorm who didn't make it past that phase

-Lobster Johnson made it past the initial brainstorm list but was an early cut when I started paring down towards 12.

-M

If I'd known that Tales of Asgard qualified, it would have been on my list.

Man...I would have loved a chance to slag him in my comments.  

I initially considered, but rather quickly decided against the Inhumans (the 1970s series by Moench, Perez and Pollard) and Hawkeye (the first 1983 mini-series), mainly because I just haven’t read them since about the early 1980s.

A few that I considered a little more seriously but nonetheless didn’t make my final cut included Fat Freddie’s Cat, Silver Surfer (the first 1960s series), Nick Fury (the Steranko material from the 1960s) and the X-men origins back-ups, specifically the Cyclops cycle (which were reprinted in the revived Amazing Adventures in 1979/80.

A few that just plain didn’t occur to me, or that I thought of too late (i.e., about half-way through the 12 days, so I couldn’t really figure out where I could slip them in) include Hercules (esp. the first mini-series from 1982), the Legion of Super-heroes, and Franklin Richards, Son of a Genius.

And finally, there are a few that I have but still haven’t read, e.g., Walt Simonson’s Orion (which I suspect would have been my no. 1 or 2 pick if I had read it), several of the Love & Rockets spin-offs that are collected in the various reprint tpbs, and Radioactive Man (I started reading my hardcover collection just before the 12 days started, but then set it aside as I started re-reading a bunch of my picks).

And finally, one that came to mind, also a bit late (so I didn’t even bother ask Kurt about it), is Steve Gerber’s Nevada, although I’m not sure she could really have been considered a ‘character’ prior to the mini-series in the 1990s, as she appeared, unnamed, in the background of a single panel in that infamous all-text issue of Howard the Duck.

His Bat outfit is one of the single worst costumes ever in comics.