[ChrisFoster]

The models you'd use for map making are often really simple. For example, the Australian plate motion model is a "seven parameter transformation" - three translations, three rotations and a scale factor. The deformation errors which can't be modeled with this are roughly centimeter level over decades; see https://www.researchgate.net/publication/258401581_ITRF_to_G...

For anyone using these kind of transformations, the boundary between the preferred models for two countries may well be discontinuous!

Ultimately the correct way to deal with this is to use a global time dependent deformation model. Some countries with large internal deformation have already gone to the effort of producing local versions. For example New Zealand: https://www.linz.govt.nz/data/geodetic-system/datums-project....

I guess there will eventually be a high quality global deformation map available but I wasn't aware of any such thing in general use as of two years ago.