Are our Assault Gun III books plagiarisms?

In the internet forum Missing-Lynx a certain Mr. X, writing under the pseudonym "Jack Reacher" and using a hacked IP-address of a friend of us, stated that both our StuG books would be plagiarism (copies), using books of Thomas Jents and Walter Spielberger, the drawings we should have stolen from Hilary Doyle's publications and we should have only modifyed them a bit before publishing. Altough the dicussion moved into a good direction for our work and us - thanks a lot to our readers posting theyr opinions! - we'd like to place our statement here:

Right from the beginning of our research, we decided to base on primary sources and not on existing literature, to avoid falling in the same traps as other authors did - perhaps we found new ones? The list of sources you'd find here.That we own an know most (if not all) of the existing StuG literature, our readers can be sure. The list of literature is published in Volume I. In addition we'd like to diagnose, that Spielberger's book, with aprox. 140 pages covering the StuG III (the other part was about StuG IV, support vehicles e.g.) was the longest piece of writing about the topic, all other publications were much shorter. It would have been quite tricky to publish some 600 pages just copying the other authors, would'nt it? The photographs we used were from our collection, some archives and lent by some gentle, well known photo collectors.

Concerning the drawings we wanted to publish, we decided to start with a blank sheet, working from scratch. Mr. Hilary Doyle's drawings were absolutely no root for these drawings, not to speak of "modifying them a bit". In addition to that, we publish more and other drawings (most of them in Volume II), than any other author ever did. The differnces between Doyle's and our own drawings are so evdent, that Mr. X must be blind:

Sample drawing Doyle

Sample drawing History Facts