It looks like the Bavaria example would have paid for a call between 3 and 5 minutes in length.
The Belgium link in 22crows' post shows a large se-tenant attachment that I had not seen before...it is mentioned but not pictured in my Yvert. There is pricing for 'mint with', 'mint without', and 'used without'.
A momentary bout of catalogue blindness has lifted, and I see that Yvert calls for these to be perf 11.5. Someone with a COB catalogue have a more complete reading of what is going on here? I have a handful of examples and they are all imperf.

[edit: I had a chance to check Byrum, and his listings match Yvert...no mention of imperfs.]