Or simply it is just "a specific product for a specific market" - as per distribution policies.
To me, that is not "custom blade", as they "mass produce them"
Custom blade = manufacture 1 unit only..... which will never be the case for retail business (the mold + legal requirements will just be too expensive). But again, it is doable - but to save on legal fees, NDA's must be in place. ie with they contracted players.
This is not just Butterfly, it applies to all brands - just like you get special Stiga blades in Chinese market, and not available any where else - ie Sweden.
Same applies to Yasaka - specific rubbers for China, that even Yasaka Sweden staff didn't hear before (asked me, what is that....)
Something small is like - Butterfly NA don't stock 1.7mm rubbers, thus it is "unavailable", not because it is "non existent"
Sadly, Butterfly products with the "special market" policy + fixed for local market only policy, makes it unfriendly for consumers.
Source:
My direct dealings with Butterfly, Yasaka, Xiom, Yinhe
My inside knowledge of table tennis in China