I hate to say it Gator but it does look modern... I didn't get a good look at your find until I got home and pulled up the photo on my home computer. I was looking at it on my cellphone originally and it was hard to tell...
It doesn't seem to have the "proper" patina for what it's age would be as shipwreck material and the folded edges don't "fit" for having been a square of hull sheathing.
I however was unaware that square nails were being used to secure copper flashing to pilings... Learn something new every day... Never really paid much attention to pilings other than to avoid hitting them with my boat... Hehehe.
Anyway Gator, when you ask people for their opinions on this forum, usually you will get some decent responses mixed in with some not so great ones sometimes. I don't think the guys who responded to your inquiry about this find are being misleading or are trying to rain on your parade so don't be offended by their responses. There are lots of people with varied experience levels on here henceforth, their responses to your inquiries will be varied... But I have found that those that are genuine and knowledgeable here have been most informative.