Wrong. Bitmains covert AB was never used on the main BTC network. That is a very different thing than the chips having the circuits in them but never turned on. BM never said anything about if the chips have AB circuits in them, they just said it was never ran outside of TestNet.
When any sort of AB is used it changes the block version number and NO blocks ever show that change before Dragonmints came online.
That is incorrect. Covert AsicBoost does not use version rolling, but instead uses a method called "
merkle grinding." Merkle grinding does not produce different block version numbers like version rolling does, hence its "covert" label. Gregory Maxwell described this method in much greater detail
here.
We do not know with absolute certainty whether Bitmain used covert AsicBoost on Bitcoin's mainnet. There are signs that suggest they did. For example, merkle grinding tends to produce empty blocks, and Bitmain's pools do have a notorious history of mining empty blocks. Also, covert AsicBoost is incompatible with segwit, and we know that Bitmain did everything they could to prevent segwit's activation on Bitcoin. But beyond those signs, currently the only way to conclude that Bitmain did not use covert AsicBoost on Bitcoin's mainnet is by taking their word for it.