question of cpu and psu

we upgraded from 10g to 11.2.0.3then applied the latest patchset (at that time -- this was last year) -- psu was 11.2.0.3.3

now i know i need to apply the security critical patch...

i read that if you had applied a patch set (which is what i think 11.2.0.3.3 was)

that you had to apply patch set updates for securities after that...

is that true?

or can i apply the oct2013 critical patch update cpu  and not the patchset update?