As I said, it's complicated. All 3 names apply to the same birds in Hong Kong, where the taxon occurring is stejnegeri.
Common Stonechat Saxicola torquata stejnegeri was the official name until recently
When the records committee recently accepted the IOC list for HK, this was split and the form in HK is know as Siberian Stonechat Saxicola maurus stejnegeri.
IOC have now split this, so that the form in HK would be Stejneger's Stonechat Saxicola stejnegeri
But these are all just different names for the same thing!
I hope this helps
