When Hermes was sold in 85, I'd be astonished if any design info pertinent to her previous catapult and arrester fit still existed, let alone was transferred!
As for the Chinese, there's an interesting article in Jane's Navy International from the end of May last year that stitches together how they got to where they are. It suggests that the ex- HMAS Melbourne was purchased for scrap and on arrival in China, the PLAN were invited by the scrapyard to have a gander, which was swiftly followed by an order to remove all useful items for further inspection and research.
Whether true or not, doesn't really matter. The principles of design and operation are known and in open source. After that it is just a question of engineering through the problem, which is a question of time and money. Where you tend to get held up is figuring out either the metallurgical tricks or the dynamic elements like hook skip. Access to the kit or elements of design info lowers that time or cost.