Some updates:
I played some more with 729 Broken Boundaries. Don't observe any change in behavior, but I am catching more differences with H3N BS. BB is easier to engage in looping, but still requires the same movements as typical chinese rubber. Block is better than H3N, chop, push and service reserve are mostly the same. Control is dropping on very hard hits, but is better than boosted H3N OS. I boost a piece of rubber scrap with 1 layer of Falco Platinum and the hardness drop from 51 to 48-49degree with permanent dome. Definitely not the same sponge as H3.
For a couple of months and less than 15 hours of play, B3 Purple shrinks a lot with a huge negative dome. The hardness jumped from an initial 54 degrees to 56 and my educated guess is that the rubber was regular B3 with a drop of purple paint and factory boost. 3 layers of Falco Platinum bring back the hardness to 54 and lower most of the negative dome. My final conclusion for this rubber: not buy, go for B3.