This review (http://operetta-research-center.org/opera-rara-la-princesse-de-trebizonde-offenbach/) by Christopher Weber (Jacques Offenbach Society Newsletter #105) on the website of the Operetta Research Center calls the new double CD of Offenbach's La Princesse de Trébizonde "as complete a version as is possible". The link to the release is at the very end of the review, the whole recording is also on Youtube (https://www.youtube.com/watch?v=FpVvthJFseE).
Judging by what little I've heard this won't exactly be a feast of good singing, alas. I have the feeling that the generation of singers who really sang this repertoire well is no more.