syspatch(8) return values?

There's no mention of what syspatch(8) returns, in the manpage.

I can prove quickly enough that it exits(0) when there's nothing to do,
but I'm more interested in knowing (for automation purposes) what the
return values are in other circumstances, and all my systems are already
up to date. Before standing up yet another system, I figured I'd ask
here.

I can think of four scenarios syspatch(8) perhaps ought to distinguish,
at least I'm interested in these 4 outcomes:
1. nothing to do
2. patches waiting, but didn't do anthing
3. patches applied
4. something went wrong

Can I reliably tell based on $? or do I have to parse the output?

Thanks,
-Adam