Why isn’t there a PRV on the water heater?. Hot and cold reversed on the lavatories is weird.
The insty is missing a vent and the sinks are missing drains too. But I agree, the most obvious is the hot/cold reversed which is a material defect according to InterNACHI SOP. 
The vent exhaust is integrated into the tankless water heater. I don’t see a requirement for drains as this is an illustration for domestic water pipe only.
Why doesn’t the image show the energy source on the small water heater? Who cares?
Which makes your point of the missing.PRV moot.
If you really want to split hairs the T fittings should not be depicted as a sanitary T.
In plumbing it’s ‘splitting hairs’ but if this was electrical the sky would be falling!
The PRV is directly attached to the potable water system. That’s what this illustration is showing you. You’re having a real difficult time with this one, aren’t you?
There are several questionable things on this diagram..
- most obvious is hot/ cold, even though they got the faucet handle colors correct, haha
- the supply to the tank water heater is also on the wrong side (cold is usually on the right)
- I assume the pump is being used for re-circulating, but when there is a demand for hot water, the supply coming from the tank will cut down the demand coming from the tankless, and it may not kick on if the flow is too low?
- and why is there an air vent? It’s a closed system, hence the expansion tank? Just curious
Thanks, everyone! The image is being updated!