Sorry, I don't get it, maybe the weekend was too tough.
Isn't this the ordinary "switch to a busy frequency" in busy times anyways?
This is what I would expect in reality.
ATC: XXX Standby for Maastricht on CHN (short form of: XXX switch to Maastricht frequency CHN, stay calm until called, they are quite busy there)
A/C: standing by for Maastricht in CHN XXX (confirm CHN, also made optional by the NOTAM - which is the minor point I am not with, as it adds a shortcut in radio and cuts confirmation at the same time, although this is done already anyways, it should be the exception, not a NOTAMed regular behavior)
- switch to CHN
- keep mouth shut until called
What if, you are never called and about to enter the next area ... they forgot about you or they are too busy, or ...