I only say it because I have never seen anyone with a miner version before its released to the general public - outside of a few test models for people to test/review. Is it totally possible they do as you say? Yes. Heck - I wish I was one of them, I would kill to have a thousand or so of the new 7nm miners.
I am still hoping that Triple-1 pulls thru and releases theirs.
Bitmain is a Chinese company. They operate on different cultural principles than other global companies. Relationships to a Chinese company are everything. It would be considered an insult if they didn't offer the first, early versions of their miners to their friends and others with whom they have a close relationship. So unless you are Chinese, you will never see anyone with an early version. That doesn't mean it doesn't happen. This is a very normal practice for Chinese manufacturers. Relationships are even more important than money to them in many ways.
That said, I spoke with some techs at WDMS summit in Georgia last month. Bitmain definitely has 7nm engineering samples back from TSMC already, and may already have the first production run. That doesn't mean you or I can buy them yet, but I would be shocked if the Chinese are not already mining with them.