I mean, up to the legal statute of limitations they can do that right (eg if they had speed camera recordings that they realized were accidentally unreviewed, they could use those and issue tickets without it being much of a morality issue).

It is maybe unfair because of a sudden burden and no ability to change your behavior before it added up to a huge sum, but it doesn't seem to have anything to do with privacy.

With failure to pay eventually landing you in jail.