Based on what I saw, I'd estimate Bitmain was replaceing S5's with S7s for 2 months at most, and possibly with S5+ for a month or two before that (and then likely sold those S5+ as "new" units once they got the S7 into production).
I don't believe for a microsecond that the S7 has been in production for 6+ months.
When you say what you saw what are you referring to? Did you get to see a plant? Just hashing online? What specifically?
"Used" S5 sale.
Hashrate fairly stable for the first part of that.
ETC.
If the S7 had been in production for 6+ months, there would have been a much longer and bigger hashrate bump due to Bitmain using them internally.
I would say before they sold the used S5's they likely had the chip design ready for S7's and likely working prototypes. I thought you had a inside source or saw something we didn't the way you worded you saw something.
It's really speculating not "seeing" i think that you are doing. Just as I am doing.