With a new production line, wafer starts are very low, and the line is long, and initially there are gaps in the line, so more starts fill the gaps until you have a decent coverage. This is why 1K-5K per month is a guesstimate, and not necessarily predictive of health. Many wafers get reworked, scrapped, lots get split up, experiments run, which makes the overall capacity, which assumes a steady state which definitely does not exist, just a made up number.
The above is all just standard semiconductor engineering. With 18A though there is a wrinkle; the advanced packaging is truly worthy of the name advanced. The BSPD process is being done in yet another facility I think, possibly New Mexico? So F52 and Mod 3 wafers aren't really complete until the BSPD facility completes them. That's where you would look for a clear signal of health I think. A steady capacity from the advanced packaging fab.