I had the chance to have a look at a scan of an advertising leaflet from FSV from the very early days. It shows the basic and expert set, and the modules Blizzard Pass, B2 and B3 in first print covers, and then goes on to show the module B 4 (Lost City) and X 1 (Isle of Dread) in the same first print cover style. To my knowledge, these modules were never published in that style at all. I recall seeing X 1 advertized somewhere else in that style, but AFAIK never actually printed that way. My best guess still is that the change in printing style came in early 1984. So, that advertizing leaflet would have been from 1983 as well, I think.

stebehil wrote in The history of german D&D/AD&D as I know it:Regarding "Gruft des Grauens", I noticed something odd a while ago. I am collecting information about the copies, but only got some minimal info about 20 copies so far. All these copies are numbered below the #500, the highest number I recorded so far is #497. With 20 copies accounted for, one should assume that the distribution is somewhat evenly among the thousand numbered copies, but instead, I got eight in the #2xx range and five in the #4xx range. I´m starting to suspect that the higher numbers weren´t even distributed.

I concur with your observation. Based on public sales, secondary marketplace archives, and collector threads, here are the numbers I've verified & documented:

034
077
108
227
241
269
299
304
311
337
338
424
457
468

The user "T.Dorst" on RPGnet commented on having #731 way back in 2009, but I wonder if it was actually #131 or #231 due to how easily handwritten European digits can be misread. I haven't inquired. He's still active on RPGNet.

If anyone has additional verified numbers, please provide them. Otherwise, it appears like any numbered copies beyond ~500 might not have been distributed and could have been destroyed. I haven't seen many of the numbers from 1–200 show up either.