It appears there are some small disagreements between the website and the attributions of the auction houses and/or the Flon catalog, all of whom seem to place this coin starting a bit later. I can't say who is correct. Maybe there is some new scholarship?
It is difficult to see any significant difference between the photos on the website for type 3/ 4 and type 6, except in the size of the city coat of arms, which of course could be die variation. The website says the way to disinguish type 3/ 4 is by its lower purity (but they do not say how much lower), and by the occurrence of spelling mistakes like OIVITIS, etc. which are not shown in their photo or on your coin.
It would be easy to accomodate this in the existing Numista listing which already has the undated (type 7) and dated (type 8) varieties wth the same design features.