Hi Emil. This is an interesting point because in the literature I have found multiple (many) possible transliterations for Úr (u, y, o, ø, v, w) as well as for Oss (ą, o, æ). If you think that o is more common for Úr, I will change it for the next update. I hope you can send me a source for this information at maartentrompper@freedom.nl. Thank you!