The legend on this site is a joke.
It's almost impossible to see the colors under the numbers, as they're only a few pixels wide: https://i.imgur.com/k8k394D.png
Trains don't even notice that. Russian wagons with nominal gauge of 1520 mm are an everyday sight on the Finnish rail network, nominal gauge 1524 mm. And yes, regardless of sanctions.
Gauge differences less than ~25mm are considered interoperable to some degree. At a 4mm gauge difference, that's basically less than the tolerance for even the most demanding high-speed track.