So, in Italy (where I'm from) they changed the law two months before I got my B licence, in 1991.
Before then, a B would allow you to drive any bike, whereas after the change you had to take a written and driving test for the first A (125cc I believe?) then another for 600cc etc.
Long story short, I couldn't drive bikes above 50cc with my B.
Fast forward many years, I moved to the UK, converted my B to its British version, stayed there 12 years, then moved back to Italy and made the conversion again.
I didn't pay any attention to it, until a couple of years later when I walked to a shop to buy a scooter.
They needed a copy of my licence, so I picked it up, turned it around and noticed that it included the A as well.
"Hold on a second, what can I drive with this?"
"The guy has and look and went "EVERYTHING", so I said to forget about the scooter and bought my first bike instead:)
Basically someone at the licence office fucked up when they converted from British to Italian, I never took any test. Oh well.