This Entertainment This Month ad ran in Marvel’s April 1992 comics. There's no mention of the Image name, and the ad is grouped with Marvel titles like Ghost Rider and X-Men. The copy reads "Hot new team of mutant heroes created, written, and drawn by Rob Liefeld!" My first impression was that this was a new X spin-off, which I'm sure is the goal of the ad ("mutant heroes"?). The $2.50 cover price is exactly twice the price of Marvel's line at this time. I saw this ad and vowed that I would not buy another mutant book, especially not one that cost the ridiculous price of $2.50. I thought that Marvel was nuts, releasing another X-book that no one could afford. I was still buying comics at convenience stores and had no access to fanzines, so the first time I learned about new projects was from these Entertainment This Month ads.
Looking back on old Usenet discussions, the earliest reference to Youngblood I can find is in October 1991. Apparently, Rob Liefeld announced another series in CBG called The Executioners. Marvel supposedly threatened to sue, leading Liefeld to announce Youngblood instead. In October 1991, X-Force was only in its fifth issue, and Liefeld was already announcing a new title.
It’s interesting to read some of the early discussions speculate over whether or not Liefeld would actually leave X-Force. Even when the solicitation for X-Force #12 is released, the same month Youngblood #1 is on sale, people aren’t sure if he’s really left the book permanently. Everyone seems to remember the Image guys announcing their books and leaving that second, but it didn’t exactly happen that way. Even after the Image announcement, a Comics International article is quoted saying, “Liefeld will still be doing 'Cable: High Lord' for Marvel to be released in 'late spring'; beyond that, spanning possibly 20 issues, he may take a rest from the characters.” Youngblood was still considered a three issue mini series when the first issue shipped. If those issues didn’t do as well as expected, Liefeld could’ve easily (I assume) come back to Marvel. Apparently, he was even developing a Cable solo series at the time! Everyone seems to be approaching Image cautiously at this point. The mail order retailer ads infer that Youngblood is a Marvel comic. Almost all of the announced titles are mini series. The creators are still working for Marvel and discussing future projects with them.
Searching through the old posts, you can find people complaining that the first issue of Youngblood is late. It was apparently due out in February or March 1992, but kept being shipped back until the week of April 13th. Image’s early reputation for lateness started with their very first comic.