In nearly every western country (EU countries, Canada, Australia, New Zealand etc) the samples are securely stored indefinitely - in the US it depends on the state but many do keep the samples there as well. That does not mean they are readily accessible- there have been cases of misuse but it is extremely rare.

From a DNA perspective one can only use the Guthrie test samples for about a decade after collection so yes, in a worst case abuse scenario we have cards that could be mined for DNA across a bunch of <10 year olds.

> From a DNA perspective one can only use the Guthrie test samples for about a decade after collection

Why is that? Is it because of sample degradation of some kind?

Yes - blood must be kept at very specific temperatures and conditions if you want to preserve its usefulness in DNA sequencing - most of these are dried blood cards without strong controls which makes them not particularly useful for good DNA data.

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.