> In terms of mount spec, I think Four Third and the successor Micro Four Third is open specification, then the Sony E mount later (not at launch time) open the specification.

They're not. MFT can be licensed by "anyone", Sony E can be licensed only for producing lenses under additional NDA-covered criteria. DSLR mounts were sometimes licensed in a somewhat similar fashion, e.g. Tokina had a license for Nikon's F-mount.