When the TNA-records referenced by Middlebrook and Everitt (p.787) do not clarify the situation, then as another possible source there is a U.S. Strategic Bombing Survey report (report #171) on attacks on the Deutsche Werft at Hamburg.
It should contain information about which force (USAF - RAF) bombed the yard with the FINK II pens at what dates, with a description and photographs of damage caused.

Middlebrook and Everitt also refer to these US SBS reports and name the I.W.M. as source.

Regards,
Walter