Leaping back to possible reasons why AL would not have given DG a joint inventorship of the patent on which apparently DG had done some work.
My guess is that AL believed that DG had not done this. It was really important to AL because "incorrectly naming inventors on a patent application can have devastating consequences; the named inventor and possibly the patent owner can lose the patent and all rights associated with it, including the right to the royalty stream generated from any patent licensing." (
http://www.rpitechnology.com/files/Getting_Inventorship_Right.pdf)
I think AL may have become convinced that DG was trying to get credit for something he had no right to. And, given DG's history, this was quite possibly true. Even though the pump was produced for Vecto, it was never marketed and did not generate a cash flow.
(
http://news.nationalpost.com/2014/0...in-bid-to-find-him-his-wife-and-his-grandson/)
In terms of patent authorship, if DG had been given clear instructions by AL regarding the work he was to complete (and DG was, in fact, paid for the work), and from those instructions anyone with ordinary skill in the field could have carried out that work, DG would not have been considered a co-inventor.
(
http://www.rpitechnology.com/files/Getting_Inventorship_Right.pdf)
As well, if DG believed he had made an independent modification, but had not kept records of his work, and could not provide other proof of his work, he would never have been able to make a case as a co-inventor.
(
http://www.rpitechnology.com/files/Getting_Inventorship_Right.pdf)