I agree that volume on the zero-fees exchanges is not accurate. In the other hand I can assure you that any of the Chinese exchange do greater volume than rest of the world together.

I explained this volume issue in this post.
https://steemit.com/bitcoin/@airmike/bobby-lee-may-be-wrong-btc-curiosity-series

Long story short. " printing of the volume " is a way how the exchanges protects themselves against HFT predatory algorithms (order-flow algorithms and front running algorithms). This situations are rare. The situations happens only when LPs pulling their orders from the orderbook very quickly in high volatility. This mechanism of printing is only temporary protection (definitely not 24/7). When volatility is low most of the volume is accurate. Printing is not needed.

There is lot of mystery on the Reddit and other discussions about this issue. Most of the people do not trade high volume so they don't know whats going on there. BTCC is only one exchange which haven't been using this type of protection, yet. They use different type of protection. " they do it by slowing of the messaging" you can not get confirmation of your trade in scale of milliseconds. There is plenty of solutions how to solve this problem but important thing is that we shouldn't ignore 98% of traded volume around the globe and calculate index from ridiculously small exchanges (one of them is at bankruptcy already).