and the question should rather be what is already clear about him?
It is clear that he died near Laski-Sieraków. There is only one place in the world where villages called Laski and Sierakow are located in the same area - it is in Puszcza Kampinoska, west of Warsaw. The exact date of his death is not given by VB, but VB states that he died in September of 1939 - so the Polish Campaign, Puszcza Kampinoska.
The bloody battle for Laski and Sierakow started exactly at 0:00 AM on 19.09.1939 and ended by the dusk on 19.09.1939.
German army captured Laski and Sierakow for the - most probably - first time on 18.09.1939 (taking the defensive positions there, trying to block the Polish breakthrough attempt to Warsaw - which did not succeed, as Poles broke through during the following day - 19.09.1939).
After 19.09.1939 some other Polish units or groups of remnants from the battle of Bzura might have been advancing through this area while breaking through to Warsaw, but no such fierce battles like the one fought on 19.09.1939 took place.
So my conclusion is that he was certainly KIA in Poland near Laski and Sierakow (as VB states) and although the exact date is not given (VB only says - it was in September of 1939), in my opinion it must have been either on 19.09.1939 or later.
He could have been KIA earlier for example if he was from Luftwaffe - but Emmerling does not say about such an event.
So in my opinion - definitely the Master List, even if some points might be not fully clear.
Because we agreed (at least I thought so) that the place of death in combination with the date of death is strange. Schroda /Sroda Slaska at 28.09.1939 appears to be at least a big "?".
Sroda Slaska? Isn't his place of death Samter = Szamotuły?
According to at least one German article from a respected (Nazi, but then respected) newspaper from that "historical period", there were some combats around Poznan (Samter is also there) in the late September of 1939 - they were fought between "bands of Polish marauders" and German police / rear units.
So the place of death Samter on 2x.09.1939 is not so strange as it seemed to be.
Morevoer - even if he wasn't KIA there, he could have died of wounds or whatever - anyway - it was certainly related to the Polish Campaign (he was not on holidays there, but on war), so in my opinion - the Master List.