I looked at 13 PN last night with the 12" at 188 times. Two were very small and the third was faint (see their 5'x5' DSS2 red images below).
The other 10 were easy: IC2448, NCC2867, NGC3132, NGC3211, NGC3242, NGC3699, NGC3918, NGC5189, IC4406, NGC5882
http://archive.eso.org/dss/dss