Markings on Dutch military vehicles often include a black strip with the letters 'NL' in white. Presumably this stands for 'Nederland' (as with Dutch car number plates). In some cases, this is replaced by the letters 'GE'. My first thought was that this refers to vehicles based in Germany ... unlikely, as the Dutch word is 'Duitsland'.

You are right:
Dutch based army vehicles carried ‚NL‘, German based vehicles ‚GE‘.
The black plate was used to write convoy numbers.
The ‚GE‘ is the abbreviation of Germany. English language is NATO standard, which is also used by the Dutch in international cooperation within NATO.

Thanks for that ... so I was correct, and it does make sense.