WotC hasn’t released a single D&D product after my departure that wasn’t initially planned by my team. (That will finally happen toward the end of this year.) We planned four years out, and those plans included long range forecasts that were reviewed by the print production team, among many others. Planning for the new PHB began in late 2020 and we were advised, even then, our forecast was large enough that the job would almost certainly require multiple printers unless we could send the book to press much earlier than usual. And yes, we usually reserved “slots” at various printers at least a year in advance. We didn’t know the final margin on any book until around a year before it was printed, but we made educated estimates of margins long before that (and those estimates factored in things like rising paper costs). In my time on D&D, these initial estimates significantly deviated from the final margins just once, and that was a dice product.