Can equipment deeper than 190mm overhang the back of the shelf?

Yes. The platform does not have an upward rear wall, so a deeper device can extend beyond it.

What matters is whether the device remains properly supported and stable, and whether the cabinet still has enough depth for the device, connectors and cable bends.

A little rear overhang can be perfectly sensible; turning a shallow shelf into a diving board for a large, rear-heavy appliance is rather less so.