I do flights of my own aircraft into China frequently, and documentation for permits is a matter that takes care from all concerned, HKG, JPN, and SGP are particularly careful with documents. China may be coy on the matter but they have a lot more to lose than gain by permitting the breach that occurs with the Russian use of aircraft contrary to both lease breaches, which run close to grand theft, and a complete disregard by Russia of Annex 8. A majoritry of these aircraft will be illegal to operate into any signatory airspace either now or in the very near future. It certainly begs the question as to who is insuring them. Nowthere are short term ways to resolve those technicalities, but one of them will become seriously limiting in the near future. There is a way around that but I have no interest in assisting the kleptocracts resolve their impending quandary.
China is a big Putin friend, though certainly doesn't want to get hit by (Western nor Russian) sanctions. As such, China does need "something" to be able to deal with both parties.
So, how to let the Russia confiscated aircraft enter China and don't get the US angry, etc. One option for that, is to take care, there are conflicting court-orders. For which China simply can say: "We don't want to take side, please resolve these among the conflicting parties". And in the meantime, we don't block any Russian aircraft with disputed ownership, access to China.
And, because these aircrafts are under Russian control, Russia can easily create the court-orders, making the aircraft paperwork "legal" again (despite this conflicting with the Western records). Russia is not interested in all the aircraft paperwork technicalities, many people here stumble over. Insurance will be from Russian companies (which probably won't pay, when things go haywire, etc).
Russia simply states: "The paperwork is correct" and when needed, will product court-orders for that. In the end, Russia is an extremely corrupt country, especially at the state level. Forget about honesty. It does not exist in Russia (nor China), otherwise, Russia would not have invaded Ukraine.......
We see the dishonest level in the extreme with the Russian army. It turns out to be "big", though completely incompetent, with from low level all the way to the top, just "Jay-sayers", not good for the reality of a strong and capable army.
Oh, and, once the Russia problem is dissolved, Western lease companies do have a big issue, to get all their aircraft back in an acceptable paperwork trail, an expensive challenge. Though, I think, in general, doable, since the Russian airlines flying the aircraft do have their procedures in place, etc, which will not suddenly be dropped, etc. So, there is a paper trail, it just needs investigation for quality and potential non-compliant repairs, etc.