How can i distinguish on the map between "perfect vmc conditions" and "no data available"?

In the screenshot there is a rectangular area, that has probably no data. This area, which was in fact not flyable in vmc, is displayed exatly the same way as the area west of the green stripe, which had in fact perfect vmc conditions.

I can see only two possibilities:

a) Weather is changing abruptly over many miles exactly on 48° 00.0 N 

b) There is a bug in the system

From some decades of real life outdoor experience, i feel free to argue, that a) is quite unlikely. 

So you are saying the system has no bugs, which again, based on some decades of IT experience, seems to me to be quite unlikely, too.

Wish you happy debugging ;-)