Regarding Dr. Moore and Greenpeace, I would think they would in fact know who were the founding members, but, at any rate, this is how they word their opinion of claims that he was a co-founder:
https://www.greenpeace.org/usa/news/greenpeace-statement-on-patric/
"Patrick Moore frequently portrays himself as a founder or co-founder of Greenpeace, and many news outlets have repeated this characterization. Although Mr. Moore played a significant role in Greenpeace Canada for several years, he did not found Greenpeace. Phil Cote, Irving Stowe, and Jim Bohlen founded Greenpeace in 1970. Patrick Moore applied for a berth on the Phyllis Cormack in March, 1971 after the organization had already been in existence for a year. A copy of his application letter and Greenpeace’s response are available
here (PDF)."
Obviously, you can click on the PDF above to read Moore's letter.
I would find it hard to believe that Greenpeace would put out this statement with a view toward slinging BS just to disassociate themselves from any connection to Dr. Moore. If he were a co-founder, in their view of their own history, admitting as much would not reflect on their own purpose and mission. They could simply portray him as one "who went astray" or however they would wish to word it. It would not reflect poorly on them at all. From the statement above, it would seem they were clear that there were three individuals regarded as the founding members. So I don't see why they would feel they would need to lie and re-write their own history. If he was not a co-founder, on the other hand, I can understand why they would want to make that fact clear, given their attitude toward climate change, and those of Dr. Moore.