It is a Sandman, not an XX7. XX7 is one of the option codes used for the Sandman special vehicle package. There are basically 2 packages:

Sandman (option codes XX7 (pre 10/75) and XU3 (post 10/75)).
Sandman with passenger tyres (XX7 post 10/75).

Same way a HQ SS sedan is still a HQ SS sedan regardless of whether it has XV2 on the body plate.