According to Wikipedia[1], "Angola" was (allegedly) to be printed on the notes later:

[T]he contract had specified that the word "Angola" would be overprinted on the new notes when they reached Lisbon and before transport to Angola (they were allegedly for colonial circulation only)

The article has an image[2] taken at the British Museum showing a real and counterfeit note, both with the same serial number.

[1] https://en.wikipedia.org/wiki/Alves_dos_Reis

[2] https://en.wikipedia.org/wiki/File:Counterfeit_500_escudo_no...