Pix you tells that if the mobile turned off VLR takes more time to detach dead mobile. But as I know there is parameter named
“IMSI Attach-Detach Allowed (ATT, Attach-Detach allowed)”. If you set ATT=1, when you switch off the mobile, it sends acknowladge message to VLR and HLR.
So, I agree with your 2 examples (MS out of coverage or out of battery ) but not this one (turned off).