Do I need to back out previous versions of a patch?

No, unless otherwise stated in the patch README.
If the previous patch installation saved the old
files, you may want to reclaim that space.

Patches can be backed out with (Solaris 2.6+):

patchrm <patch-id>

or in earlier releases:

/var/sadm/patch/<patch-id>/backoutpatch <patch-id>

Backoutpatch can take an awful long time, especially when the
patch contained a lot of files. This is fixed in later versions
of backoutpatch.

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