As far as I know (I don't collect) Jeremy was the only static PID from the 3rd gen. Usually the Event Pokemon were Common GBA [un]Restricted, a modified Method 1 generation method in which an initial seed frame 1 method 1 flipped PID is used for the IVPID.
For the ones that are unknown, they are unknown. They may or may not have a relationship, so it is your risk to assume that they don't.
In Gen 4, static PIDs ensured Nature, Ability, and Gender. IVs were never set in generation 4. If the PID was unset, it would be generated with the IVs (Mystery Gift PID).
In Gen 5, there is no longer a IVPID relationship due to IVs being untied from PID for every ingame generation method. PIDs are generated with a simple XOR of an in-game RNG seed. Ability and Natures will restrict the PID generated, in ways we have yet to document.
In conclusion, Unknown GBA types (MAY) not have a relationship [WISH ones]. Gen 5 will not have a relationship.