The "no need" is so patently false. Notwithstanding the obvious privacy implications (your data belongs to you), first thing asked for if you are in the ER bleeding? Bloodtype.
If there is a major haemorrhage the patient will receive the universal donor (O-) while the test for definitive blood type is performed.
Is that not the case?
Had they asked, I would have given the wrong answer. My blood was typed when I was born. 25 years later when I started donating blood, I was typed again -- and told a different type.
My physicians and phlebotomists assure me blood type cannot change, and old blood tests were simply not very accurate. I don't know any lab or clinic that trusts what someone else claims about blood type.