There has been some evidence that DNA can be preserved far longer than the half-life would suggest.
If the DNA molecule is immobilized in a solid, either by freezing or by extreme drying, the half-life will be much longer.
That half-life was for bird bones preserved at 13.1 Celsius degrees.
Even in this paper it was mentioned that at minus 5 Celsius degrees some information from the DNA should remain even after 1 million years.
Unfortunately, there are very few, if any, places on Earth where ancient DNA would have the chance to be preserved for a long time either by freezing or by extreme drying.
The paper that started this thread was not about the decomposition of the individual nucleotides, which might be preserved even from dinosaurs, but about the speed of the fragmentation of the DNA molecule, which causes a continuous loss of information until the fragments are so short that no useful information remains.
I certainly hope that we will find cases of extremely lucky preservation of long DNA fragments that are more ancient than what was found until today.
Until now, the oldest DNA that was preserved well enough to allow sequencing of significant parts of it had an age of up to a few tens of thousands of years, e.g. from mammoths, woolly rhinoceroses, cave bears, cave lions, Neanderthal humans etc.