I can't tell you about each month but I bought my mother a Z3 Compact around 14 months ago. It got Marshmallow ~6 weeks after its official release, and will have Nougat pretty soon now (so I heard on the net).

Even though I dislike Sony recently, they were awesome -- up to their Z3 phones and Z4 tablet releases. And they don't abandon their devices as quickly as everybody else.

Err, my Z3 didn't get Marshmallow until more than half a year passed from the release date.

Marshmallow was released in late October 2015 [1]. Meanwhile, the Z3 only just started rolling in early April 2016 [2]. That's pretty mediocre if you ask me.

[1]: https://android.googleblog.com/2015/10/get-ready-for-sweet-t... [2]: http://www.androidpolice.com/2016/04/09/marshmallow-update-r...

That's very weird because I clearly remember my mother getting the update around the end of January 2016. OK, it's not 6 weeks, I remember the wrong release date then (thought it was mid-Dec 2015).

Eh, anyway. Peculiarities with the release schedules are sadly the norm.