It’s quite normal to name amps in this way, whether it’s a combo or a head, and no matter the manufacturer. And again, even GK rates combos like this. Look at this screenshot from the GK website:
View attachment 4040188
Now, the MB 210 puts out 500 watts
only with an extension cab at 4 ohms. But look how they write 500 in large black lettering and the almost indecipherable legend «@4O W/ext» in small grey lettering. What you get out of the box is 350 watts. To find that out, you actually have to read the manual.
Any combo that takes a passive extension cab works in this way. And every manufacturer that makes them, AFAIK, rate them at the higher 4 ohm rating (with extension cab), with the actual «out-of-the-box» output hidden in the small print, GK included.
The MB 212 is an exception to this rule because it uses an active extension cab. Only two mainstream manufacturers I know make combos that take active cabs, Blackstar being the other.
Whether or not this way of rating amps is misleading is hard to say. Maybe. But if so, the whole industry is doing it, so at least it’s consistent.