I'll add a new game as soon as I know that it has shipped, as that is the date we use for the new listing. (The production start dates are considered proprietary and are not shared by the "major" manufacturers.) In almost all instances, I have the listing all built out and prepped and ready to add, just waiting on the date as proof of shipment. Most often, it is the manufacturer who tells me what month/year that shipping began for each model. It rests on me to stay on top of asking them, as they do not notify me. In instances where that does not timely happen, usually a user will email us to ask why is the game not shown. By that time it usually means the game had shipped so I'll go looking for evidence that it has. Could be as easy as asking the manufacturer. If not, and if the person who contacts us is an owner of the new game, I'll typically ask as proof a picture showing the game set up in the residence (as opposed to an undated picture found anywhere online of a carton sitting on an unmarked dock). At least that way I can get the year as a date, and may later successfully determine the month that shipping began. (Useless hint: if you see games on the IPDB from, say, the last ten years that show only a year and no month, that likely happened because communication between me and the manufacturer for those games was not optimum. No judgement implied here.) In the last several years, the major manufacturers have been quite responsive in helping me build quality listings. It certainly helps that their own websites feature more information than they used to, years ago.
In the interests of fair disclosure, I will tell you that last month I finally added three games made in 2018 because the not-major manufacturer was not responsive to my repeated requests. And I finally forgot all about them, focused instead on productive work.
Hope this helps, if you return here to read it.