There were actually two variants of the Honda CX500, GL500, CX650 and GL650 (including Turbo models) automatic cam chain tensioner blade. Apparently the change was not brought about because of a functional difference between them, simply a change in part supplier to Honda.
Looking for the differences between the auto and manual blades instead? See this article instead.
The two relevant part numbers are 14511-MC7-000 and 14511-ME2-000. The MC7 unit (What does that mean? See the Honda Product Codes) is the skinnier one that you see reproduced at David Silver Spares.
The ME2 unit appears substantially thicker!
The guide part numbers appear to not differe between models like the tensioner blade does.