The legal successor to the USSR is the Russian Federation which also inherited the UN seat, if the intellectual property of the projects in the USSR were of the state, they should automatically pass to the Russian Federation.
I don't want to derail this thread too much, but since it is still J-15 related I will elaborate.
Yes, Russian Federation obviously inherited most of the USSR property and political status.
As I said, from the Russian perspective, it is probably no doubt IP of UAC.
However it did not inherit ALL property of it. To use another example, the valuable Tu-160 Blackjack bomber was passed to Ukraine and later "purchased" back by Russia. Thus even Russia had considered it Ukrainian property.
Back to the J-15 now. This might give insight to Gatekeeper as well. I am not a lawyer, so take it as you may. A lot of intellectual property is a grey area even for Western countries. Why was the T-10K prototype in Ukraine? Because the Soviet Naval aviation research office was in Crimea, where they also built the aircraft carriers.
Normally in a Western country, this sort of stuff is spelled out very clearly in contracts. The employer retains all rights to the intellectual property with regards to this contract or something like that. However, I imagine that no such contract existed in the USSR. Is the Soviet naval aviation research office a subsidiary of Sukhoi? Probably not since they also were making similar modifications for Mikoyan for Mig-29K. If we can establish that the office is an independent entity, what sort of rights did they retain to the work? Basically an impossible question.
The idea of reverse engineering is too simplified in most peoples' mind. It's not like you just kind of take it apart, do some measurements, photograph everything, make some CAD files and off you go. We don't know the exact differences between Sino-Flanker and Russo-Flanker (Even between IAPO and KnAAPO, it is said that KnAAPO is better). However, it probably is kind of significant this point. Almost all the electronics would be different for one. Another would be China does not have the access to the proprietary Russian Titanium machining (Even Boeing 787 is using these parts), so it is known that some of these parts have been substituted with composites.
Furthermore, and this is the thing that really trips up Western countries' legal systems, you cannot really control someone's knowledge. A lot of these Ukrainian engineers/designers were legally hired and paid to work on the J-15. (In the software industry, they make programmers sign non-compete agreements and just hope that whatever they were working on goes out of date by the expiration). Prototype in hand or not, these guys would be familiar folding wing mechanics, structural stress analysis, any caveats experienced during development, and likely were able to help with material selection changes in the cases where they have replaced Russian-spec parts with different Chinese ones.
This topic is of some personal interest to myself because I had started to look at PLA when Su-27SK (J-11) was brand new to PLAAF. I don't think anyone on those early PLA message boards foresaw a whole family of Sino-Flankers. A huge concern at the time was that the N001 radar even back then was not really state of the art, especially since Bars PESA was sold to India. As such, you can see the amount of work put into projects like J-15.
