I've never seen a disc tab design like that, one little boss on each stay.
It's not uncommon but this one is unusual as they've used the old IS standard mount.
High volume builders would swerve it because the ability to position the calliper can be affected by the geometry of the stays and the design of the calliper. And Flat Mount solves it completely, obvs.
These tabs I’ve had added don’t exactly conform to the ISO standard; I had them positioned so that the Hope ‘Number 5’ IS caliper designed for a 140mm rotor can be used with a 160mm on the rear without any adapters.
It's not uncommon but this one is unusual as they've used the old IS standard mount.
High volume builders would swerve it because the ability to position the calliper can be affected by the geometry of the stays and the design of the calliper. And Flat Mount solves it completely, obvs.