2531.80 typo differences

Hi all,

I was reading some old topics on this forum and looking at some photos of the internet, and a question arose regarding the typography of the 2531.80 models. From what I understand, they follow this pattern:

1. Asymmetrical "3": found only in models with tritium, manufactured until 1997.

2. Symmetrical "3": found in some tritium models and in all Luminova models.

Does anyone know when this symmetrical "3" appeared in tritium models?

Photos follow for better understanding.