I stand to be shot down in flames but here goes……..

Dot 5 is purple so really there should not be a problem deducing what’s in your system.
But my understanding is the purple colour is not permanent and after a few years the fluid will be more of an amber colour.

Hence, why people do the “water test”!

Regards

Geof
70th Anniversary 4/4 (Duratec 1.8), model 1995