When does EXIF data get lost?

I suspect I'm being unduly optimistic in hoping this is a question
with a relatively simple answer!

When I browse folders of old photos, I would often like to know the
precise date and time they were taken. But the EXIF data is missing
for many. Presumably EXIF info must have existed for *all* of them
when I first downloaded the DSC000xxxx.jpg images from my Sony
Cybershot DSC-1 to my PC, but editing has destroyed it?

Does anyone have or know of an up to date list of all operations by
specific graphic editing programs which result in such destruction of
the EXIF data please, so that I can make a point of avoiding them?

Am I right that although Operation X in Program A might preserve EXIF,
Operation X in Program B, or Operation Y in Program A (etc) might
destroy it? IOW, it's something of a mess? If so, I guess the safest
bet is to keep a copy of those originals, or at least a compact list
of some sort of their EXIF dates, for future reference if it's
inadvertently lost?

--
Terry, West Sussex, UK