I think the help is provided but not significant. The fact, antonov main product share no lineage of their legacy and product hardly convinced us antonov involved in major designing of Y-20. In fact , Y-20 share more similarity to C-17. The fact, its chief designer did not mention anything about foreign helps , tell us Y-20 is virtually indigenous effect. It deploy many advance manufacturing technique like 3-D printing which I think is out of the scope of antonov advise.
ARJ 21's mainwing design they had a hand in, that';s public.
these exchange and helps are normal.
china even went to bombardier for help on some projects.