An accurate summary of what happened, but some details are still missing and that is the reason I have not yet entered the metro as an unfinished project.
Metro tunnels did get built.
I think there would have been 2 series of prototypes and this is one of them. The other set would have been built earlier and also scrapped. It's a fascinating story, but here I really need to search in old magazines and I just don't have the time right now.

Интересно, сколько случаев в Мире, когда сделали вагоны, а метро не открыли? Это как минимум, второй случай. Первый мне известен Цинцинатти. Вагоны от Цинцинатти пошли в Нью-Йорк.

The story here is more complicated.
The Ministry of Transport at the time, with tons of money, built new roads and tram tunnels everywhere in the 1970s.
In both Charleroi and Antwerp, the last tunnels built at the time will hopefully be in service around 2027.
The Belgian industry was then partly subsidised by a variety of ministries, with the design of new vehicles for export being a particular objective.
In this particular case, it was about building automatic subways of a smaller size: this didn't exist then. A test track was therefore built in Jumet (near Charleroi) for this purpose. The factory (ACEC) was sold to Alstom in France. Alstom was working on exactly the same project; testing and further building prototypes in Belgium was no longer necessary.
Actually, it was never proven that the tunnels in Liège would ever be put into service. The vehicles were built as an experiment, with indeed a possible deployment in Liege, although there is no evidence about that either.
Should Charleroi possess a transport or industrial museum, the vehicle would certainly be in its place there. Of course: no problem that it's in Liège (just as the tram from Aachen) but it's really not proved that this metro was built for Liège.