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.
Why is that? Is it because of sample degradation of some kind?
“We and others recently have shown that DNA extracted from Guthrie cards (up to a decade old) or blood spots can be used to perform whole-genome methylation analysis”
You are notably omitting that those specific samples were kept at -20° C. I don’t know any country that does that for their Guthrie samples.
I'm no expert though. Hopefully others can weigh in.
https://www.nzherald.co.nz/nz/lawyer-challenges-courts-right...
and
https://www.stuff.co.nz/national/crime/97840280/parents-upse...
You can fill out a form and demand they return the samples to you.
Even if you can trust the government today, there is no guarantee they can be trusted tomorrow. cf. the abortion stuff in America.
This seems pretty disingenuous - yes you gave a blood sample (which has DNA in it) but no DNA genome sequencing is taking place - they simply check it for a series of disorders to make sure a baby is healthy and yes gather aggregate data on prevalence of disorders at the population level.