Voadam
Legend
My understanding of the Gentleman's Agreement is that it was just that - an agreement that allowed third-party companies to use WotC's intellectual properties before the specifics of the OGL were hammered out. This included projects that were begun before the OGL was finished, even though the final product went to market after the OGL had been released. Hence why you have products such as Unveiled Masters going to market in 2002, despite the OGL having been released by then (as I recall).
The OGL was finished before realease of D&D. The srd releasing D&D content as OGC under the OGL was originally only a draft document at release time that included all the MM monsters including the non OGC monsters. There was a gentleman's agreement that people could use that until the final srd was released. It was not until about a year or so after d20 had been going full steam with hundreds of third-party products released that had used the draft srd that the official SRD was released with some monsters that had been in the draft srd not included. I don't recall whether it was until the release of the 3.5 srd that the excluded monsters were officially designated as product identity under the OGL.
Black Ice Well is not alone in using stuff from the draft srd that was not in the final.
AEG's mini module the Crypt of St. Bethesda has a carrion crawler in it.
I think Necromancer Games' Tomb of Abysthor has Kuo toa and Slaad in it.
Monte Cook's Malhavoc Press' Banewarrens had beholders, illithids, yuan ti, umber hulks, and a slaad in it. I think his Demon God's Fane module had a beholder as well. His module for Atlas Games Penumbra line had a half black dragon umber hulk. His later stuff does not have these types of things in them. I expect he would have liked to have used them in his Ptolus mega-city book though if he could have.