Nice. I am a little confuse on the different types of education you haven taken. What is a professional degree?
Edit: Licence is an intermediary level between bachelor and master/doctor.
There's a bit of a naming confusion going on. First, the title Engineer. In France, many universities propose the title "Ingénieur" (Engineer), but not all have the seal of the Commission des Titres d'Ingénieur (CTI). If one wants to be an Engineer's Engineer, they must look up the University and see if the CTI sort of recognizes that degree as "Ingénieur", or a "true Scotsman".
In France this is called “alternance”. I don’t know about OP but you can have a “Licence professionnelle” with or without “alternance”; it depends on your school/university.
The "Professionelle" part is more about the fact that after it you should not continue studying but go for a career.
They get in with a different baccalauréat UFC (Université de la Formation Continue) which anyone can take even without necessarily being enrolled in high-school.
Some of those who are enrolled in high-school hedge their bet and go for regular BAC and UFC BAC. They often fail the regular BAC but succeed at the other and enter UFC which has classes inside "real" universities after hours. Not dedicated classrooms, though.
They came out of class one day and I said I've never seen them around (they didn't look the part) and they informed me who they were and talked about what they were learning, etc.
They approached me when I graduated many years ago. I don't remember the exact details but I seem to remember that they were catering for engineers doing civil engineering. ie to build bridges that won't fall down when a truck goes across it.