Using both sides of DS DD disks

["Frank Townsend" <ftownsen@iamdigex.net>]

I was reading the recent discussion about DSDD disks and disk notchers and
saw a comment by Roy as follows:

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> Now a further question is "Why are most DSDD diskettes only notched on
> one side?".

"Because a double sided disk drive doesn't have to have the disk flipped
over."
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I'm using Apple 5.25 disk drives.  Are these double sided drives?  If not,
were there any Apple II double sided 5.25 drives?

Alternatively, were DSDD disks sold that were pre-notched on both sides?

Finally, is there really something about flipping a disk to record on the
"wrong side" that endangers data on the "right side" as someone suggested in
a previous post?