Scientists have extracted usable DNA from from 7000 year old corpses. I imagine the technology exists for a decades old blood sample if it’s stored at least somewhat properly.
Yes that is very true - There is however quite a bit of difference between a full corpse that is mildly preserved and a dried fleck of blood - a big difference too between a stored fluid blood sample and these pinprick dried sample.
It's probably prohibitively expensive at the moment.