These were the cassettes that came after the Sony Dynamicron series, also known as SD. These preceded the Super DX series which was very long-lived. The jacket tries to claim that the cassette is 20% better, but does not explain just how. Their magnetic particle formulation was given the name of Vivax. This also features the quality certification mark.
These share a lot of commonalities with the SD with the shell differing in its hatching and the use of a white hub clip instead of a green hub clip. The original spine label is still affixed, which alludes to the lengths available at the time. Interestingly, this range of cassettes was assembled in Thailand, rather than Japan.