The titular crown is said to be the crown of King William II of the Netherlands, which is the official Dutch state crown. After stealing the crown, the Baron puts it on his head, which he shouldn't be able to do. The Dutch state crown is only meant for display during the monarch's inauguration and wouldn't fit on a person's head.
On the DVD Home Video Release of Liedjes in Grootmoeder's tijd Aad Klaris is credited as W. Klaris whereas in the original episodes he is credited correctly.
As a running gag throughout the series, Bassie can't tell the ringing of the door bell, the alarm clock and the telephone in the hotel room apart. But even if they would sound the same, wouldn't he still be able to hear from which direction the ringing is coming?
After B1 mistakenly gives the key to Bassie, the thieves constantly try to steal it back by burgling Bassie and Adriaan, drugging them, chasing them and setting traps. But after tracking them down to the circus, B1 could also simply asked the key back with the explanation that it was a simple mistake, which would have saved the criminals lots of trouble.
Inspecteur Jeroen van der Steen aka The Captain speaks common Dutch without a local accent while being under hypnosis, but has a very strong Flemish accent when waking up.