It has always been company's policy to completely remove any imagery of graduated talents from any merch and promotion materials. Deleting all videos from the channel is also a standard response, and Nina had to specifically ask management to keep them for at least a limited time. I know that Nijisanji doesn't deserve benefit of the doubt at this point, but the way they've been strictly following that guideline seems to imply that 'delete everything after graduation' is probably a contractual agreement between them and talents.
'Let is slide, it's not a big deal' is not how Japanese companies operate. Yes, they should've made NijiEN a separate company with Western attitudes. Yes, that's why most creative livers already left NijiEN. Yes, it's obvious to us that Mysta and Nina's VAs wouldn't sue Nijisanji for a cameo appearance. It's not so obvious to the Japanese. They likely don't have to be this strict about it (given that, for example, Pekora had Rushia in her intro long after she was terminated), but that's Nijisanji company-wide rules that everybody had to follow and Selen was expecting preferential treatment.
Reimu had Nina on her intro screen for her summer outfit, an outfit that was released almost half a year after Nina's graduation
She had a stream that very same day with Petra, where you can clearly spot a direct reference to Nina's apperance (White hair, broad hat like her 2nd outfit, fox tails and red accents) in the background of her stream start
Now, this could've been approved long before Nina's graduation, but the fact that there hasnt been any sort of edits or immediate removal of Nina's apperance, or a sort of public indication of that, unlike Selen's video that was taken down, then there are chances there arent any bizzare indications to not include graduated livers in content
Maybe this had to do something with the fact that they asked management for permission beforehand and waited until they received it. Crazy idea, I know.
Completely unrelated clip
https://youtu.be/Vu0_lFVssS0?t=2983
You can give something against Selen in that she seemingly didnt wait for permission yes, but its still not verboten to include graduated livers in new content
also, what does Phase have to do with anything, different company, different continent, retard
Also, on the JP side, Hololive still has Coco's channel up, even in the NijiJP side you have graduated livers like Warabada Meiji still have their content up
https://www.youtube.com/@WarabedaMeiji/streams graduated almost two years ago now, go to this shitty list and you can find a fair amount of graduated livers who still have content up, not everyone, and it obviously does not include terminations, but there are enough outliers to prove that they dont shoah everything a liver does upon graduation under certain circumstances