This comes up from time to time. Read the introduction. I don't have my copy available right now to get an exact quote, but IIRC it has a paragraph (second paragraph on the second page, I think) explaining that if the item is not given an explicit date, it is representative of what was (or was thought at the time to be) used in period, but is not claimed to be an actual Revolutionary period artifact. Something like 1/3 of the items fall into this category - they are there to give collectors an idea of what to look for, but aren't actually 18th century, just the best that Neumann could find at the time.
Those starters aren't dated, so Neumann is illustrating them as an example of what he thought an 18th starter should look like. He is probably right, IF starters were used they probably would look a lot like those!
On a general note, always read the introductions to history books. That is where the author sets forth the thesis or otherwise tell you the purpose for which he or she is writing the book, and knowing what the author is trying to do allows you to get more out of the book, usually.