you have to realize also at least for the gmt900's being that 3g is defunct these units at best could only receive a satellite signal, there is no transmission = untraceable.this is a very common pattern: telling people that feature X is for their "safety", when in reality it is done to surveil and control them.
other related examples: Find My feature on the iphone sends continuous gps coordinate data to apple, intel "anti theft" allows large organizations to control machines on remote, intel management engine allows for "people" to control machines on remote, search engines and social media routinely blacklist content for "safety", etc.
whether most people realize it or not, onstar - and every other default-enabled car monitoring system - is there to mine their location data and sell that data to interested 3rd parties. unless you fully disable the cellular transceiver used by such systems, you cannot even use your own vehicle without it being tracked, even if you leave your phone/devices at home.
and the k2's and T2's could be traced provided there was a 4g signal, there is no satelitte "uplink" on any publicly sold GM ehicles unless you somehow added it 3rd party, these only receive. without 4g they can't sit there on there on computer screen and watch you move around that requires a "signal transmission"
the word "onstar" leads many to believe you have some kind of space based communication, you do not.
if you crash in the mountains with no cellular service and press the blue button ain't no one coming to rescue you, your done.