1 - 20th regiment may be the unit in Syria... number unknown
2 - reminder that planned deployment by the end of 2020 is 28 regiments. That means 4 a year to complete.
3 - have not seen a S400 regiment arrive complete. They start off with the radars and C3's of the HQ plus 1 battalion of S400. They command original S300 battalions of that regiment for such time until other S400 battalions arrive.
4 - this makes it difficult to count S400 battalions accurately
5 - it is possible there are 21 regiments as there was some confusion in the unit numbers back in 2016 if you remember, or there may be a training regiment at Ashuluk.
6 - it almost appears that the S300V's serving in Air Defense are going back to Ground Forces control. Rather or not the Regimental numbers are transferring also remains to be seen. (Kaliningrad and Sakhalin) Also would not be surprised to see the S300V unit in Birobidzhan revert to it's original 203rd AD brigade name and under Ground Forces control.