[Peter Cornwell]

I cannot answer for the details from the German crash list you mention & suggest you query their sources with them. This loss was not included in Blitz T&N as no bodies were recovered by the British authorities. For the same reason, no A.I.1.(k) Report was raised thus it is not featured in the Luftwaffe Crash Archive.

1./KGr.126 Heinkel He111H-4 (6948). Damaged during night sortie to London and ditched in the North Sea 20 miles off the Norfolk coast. BO Lt zur See Günther Grünwald, BF Uffz Otto Plenert, BO Lt Karl-Fritz Schreyer, and BM Gefr Richard Weber all took to dinghy but drowned, FF Uffz Hugo Greeven rescued - admitted to hospital in Den Helder. Aircraft IT+KH 100% write-off.
This entire crew was first spotted at 7.50 a.m. by He115 M2+KH of 1./KüFlGr.106 but despite efforts by the Seenotdienst they failed to be rescued and by 4.17 p.m. only two men remained in the dinghy.