I noticed my new 2019 VW manual, it says 3 yr for the first flush, 2 yr subsequently.
This is consistent with my thinking on the subject. In new lines, there's no corrosion to resist.
imo, it depends a lot on your climate and parking. Here in the country, everything outside gets soaked with dew almost every night including my cars. otoh, my mother parks in a heated garage in the middle of a urban city heat island. I doubt fluid in her car accumulates moisture the same as me, 90 miles away.