Lee, Looking at the BB, there is a No. 6 and is dated circa 1885 - 1905. My griddle does not have the No. before the 8. Their might be a slight variation in the marking. But from what I have read and what Steve Stephens is saying that they added the No. 6 griddle later. I am not sure if they added the NO. to the # 7,8,9 griddles at a later date. The BB does not show a #10, as Steve Stephens knows best.
The first variation would have the # on the underside handle but no P/N
The second variation would have the different number on the handle like yours with the P/N added
The third variation would have the number on the bottom with the P/N, like mine
I am using the word variation, just to show the different markings, not griddles. I believe all the griddles were of the same style / variation.
Note: The BB does not show a #10, also from Steve writes, 1883 catalog only shows 7-10. The BB dates from 1885 - 1905
This is the best information I have at this point. So if I am not 100% let me know, need to feed the brain.
---------- Post added at 09:24 AM ---------- Previous post was at 08:46 AM ----------
Lee, Here is a little eye candy for you #10 Erie griddle.
http://www.castironcollector.com/forum/showthread.php?p=3159#post3159