Hi,
I made those changes, because I have seen those guidepost with R44 on them (https://www.openstreetmap.org/node/12536091967, https://www.openstreetmap.org/node/12536142713) and this one without marking of hiking route (https://www.openstreetmap.org/node/12536142712).
According to those guideposts, the current state of R51 and R44 reflects the reality.
There is no duty to inform any authorities (and there were no info on those relations, that it's ought to do that). Nevertheless, if you got the contact, please inform them. Thanks.

You can see those photos of guideposts here (https://en.mapy.cz/turisticka?x=7.4618195&y=44.3524887&z=16&ovl=2), hope that could help.

Kind regards.
V