Graham the PK catalog is
PK --- L. Perek and L. Kohoutek. The 1967 'Catalogue of Galactic and Planetary Nebulae'.
Many Planetary neb do not have NGC or IC numbers.
The PNG catalog contains 1143 PN, only 93 are NGC objects and 34 are IC objects.
PNG --- Planetary Nebulae, Galactic coordinates. This designation is from 'The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae'. This is the current 'state of the art' catalog of planetary nebula, published by the European Southern Observatory.
Kent Wallace put the PNG online at:
http://www.blackskies.org/intro.html#Files