I suddenly realised as I was reading the most recent posts that we're missing a trick here.
As you explain in the Opening Post, you think the information on the sign doesn't add up.
There are repeated comments from others in the thread to the effect of 'we don't know what (published research etc.) they based the information on the sign on'.
Surely the obvious solution is for you to contact the Museum describing your queries/concerns and ask them if they can provide further information to substantiate the summary on the sign.
Assuming you get a reply you can then share it with us (if you do it by e-mail then you can just cut'n'paste it into here to save having to type it all in
).
I wish I didn't know now what I didn't know then