Since wands seem to be somewhat sentient in Harry Potter (they can tell if their owner was defeated) and seem to have the ability to bend towards a user that favours them, I don't think laws regarding wands would be designed based on any normal (muggle) property right laws. For instance, lets say A's wand was won by B, so this wand no longer responds to A as it used to, but responds very good to B. It would not be much useful for A even if he did win it back in a legal battle, as the wand has already changed it's allegiance to B
Moreover, since Gregorovitch was in a far away country (Voldemort couldn't even apparate there, he had to fly instead), different jurisdictions would apply which would make a court case more complicated, especially since Dumbledore was a socio-politically powerful figure in his own country (requested to become the Minister of Magic) and somewhat renowned abroad as well
From the wand's allegiance point of view, Dumbledore "legally" owns the Elder Wand
Grindelwald didn't just steal the wand, he stunned Gregorovitch before taking off
We know that the wand changes allegiance even after a successful non-aggressive (somewhat) spell, such as the Expelliarmus charm
Being stunned should definitely count as having been successfully attacked
And how Harry was hurrying along a dark corridor in stout little
Gregorovitch’s wake as he held a lantern aloft: Gregorovitch burst
into the room at the end of the passage and his lantern illuminated
what looked like a workshop; wood shavings and gold gleamed in the
swinging pool of light, and there on the window ledge sat perched,
like a giant bird, a young man with golden hair. In the split second
that the lantern’s light illuminated him, Harry saw the delight upon
his handsome face, then the intruder shot a Stunning Spell from his
wand and jumped neatly backward out of the window with a crow of
laughter.
I realise that it doesn't explicitly say if the stunning spell connected or not, but I think it can be implied from the narrative that it did