That is purely your own logic, but there is no difference in real life on assessing a pt of a one car crash vs multi.
Health care providers will always make sure that there is no underlying medical problem once the apparent threats to life are taken care of.
Assessment is ALWAYS, ABCs, airway (patent or established), Breathing (spontaneous or Positive Airway Ventilation and Make sure there are no signs of tension Pneumo), Circulation (control any bleeding, and maintain MAP of at least 60)
Depending on the findings, further assessment is done according to the situation. For example if pt is is still unresponsive after stabilizing ABCs , BGL 12 lead and if possible Neuro exam.
The same is for Patients from a one car or multi car MVA. the fact that you believe (and could very be true) that pts from single car MVAs are more likely to have an underlying medical that caused the accident does not change the assessment or treatment at all.
Regardless of the fact if there is suspicion of a medical, the receiving facility will level the trauma accordingly, if necessary consider CT Scan, FAST if suspicion of internal injury and have sub specialties as needed and resources the facility has.
this is a cookbook scenario, of course each case is different and should be assessed and treated accordingly but in reality there is no difference in the amount of cars involved.