This is just about the oldest Revenue stamp I have with a clearly documented date of 08/17/1863. I believe it's an R46.

Although this particular example carries a minimal catalog value, Scott Specialized goes on to suggest that most of these stamps were issued in 1862 or 1863, making no specific reference to the date of issue of any of the individual stamps in the series. I can only assume this would have been one of the earlier uses of the stamp.
Scott Specialized goes to suggest that since most of these revenues were cancelled with pen and ink, stamped cancellations command a higher value. Would this early example qualify as having some premium over the catalog listing, even though it has a straight edge?