I don't know what's your source is but I know that it's quite strange in Morocco.
My source was mapping, Wegenwiki and the SSC thread.
The mentioned numbering scheme is according to what is signed on the roads.
which is, of course, why everyone was getting it wrong until this afternoon
I've quoted the source with pics showing the signs.
I assumed it was just the Chris Zwolle post full of weasel words about whether the Autoroute renumbering was official and declaring 'no official source' that I had read a couple of hours earlier, rather than new information.
But I'm still going to wait for something more official.
Btw, why do you call Czech Republic "Czechia"?
Because someone a few years ago demanded that I read the request of the Czech President saying "please use Czechia as a short English name". And it makes sense - we don't call it's neighbour the "Slovak Republic" (its official name) after all.
I think it's not very common, is it?
Not in English.