Does horsea always have an encounter slot of 1, 3, 5? Or is that hypothetical too?
If the frame doesn't match an encounter slot what do I do? Look for one that does?
I was just giving an example on the 1, 3, 5. Just to try and explain what encounter slots are. I have no clue what encounter slots Horsea is on in what area.
The Pokemon's encounter slots change depending the area.
If the frame doesn't match the encounter slot, find a different frame on that seed that has the desired spread, but hope that it has the encounter slot you're looking for.
As if you can't find a frame that has the correct encounter slot, that means you won't be able to get a Horsea with that seed.