We then left them be to return to nature so they would hopefully go unnoticed by folks.
Does this just mean you left them alone for 6 months then?
I’d say (according to my own interpretation of “Trail Etiquette”) anyone finding an apparently abandoned trail has fair scope to start modifying it as the person(s) who orriginally made it have not been back… obviously in your case you were leaving it to age like a good cheese, but in fairness to the much bemoaned yoofs, how were they supposed to know this?
For my own part me and a few locals near me have started re-digging some of our local woods lately, we keep finding “Yet another” old line that’s been left for a good long while. normally a nice line that benefits from a bit of creative sculpture or even the addition of a nice big jump and/or Berm…
I’m sure someone who might have dug there previously may take umbridge at our changes, but we all ride there regularly and very little changes have been made in the last 12-18 months, so far as we’re concerned we’re taking the initiative to keep the trails rideable and “evolving”…
Ultimately if you really want “ownership” of some trails you need to start a club and get propoer buy in from FC/Landowner and co…