I think the number of versions of Seisan cover a wider range than just the three versions offered.

From Matsumura
Matsumura No Seisan
Matsumura Orthodox Seisan (Soken)
Kyan No Seisan
Shorinji No Seisan
There is another version too.
Seibukan No Seisan
Shimabuku No Seisan
Itosu No Seisan
Funakoshi No Seisan

From Hiagonna Kanryo
To'on Ryu No Seisan
Goju No Seisan (many sub variations)
Mabuni No Seisan (Shito Ryu)

Tomari Traditions
Tomari No Seisan
Odo No Seisan

Matoyashi No Seisan
Motobu No Seisan
Agagaki No Seisan (McCarthy)

Uechi Tradktions
there are two different Uechi variations on Seisan
Paganoon Ryu No Seisan

It's unfair to lump them together in the quest.

The simplest basic analysis is the underlying embusen, the pattern they all share.

1. Essentially a row of techniques going out.
2. A turn
3. A row of techniques coming back
4. A "+" pattern of techniques.

IMO this much is present in all the versions. Then the issue is the embleshment, the flux, the tidal flow of the form, execution changes, and additions.

If you start looking at the techniques you are getting into the flex of the art, but if you look at the floor, you're closer to the origins (IMVHO).

Every one of these variations is a complete art in themselves. No source version is necessary. But there can be further analysis towards universal underlying application that spans the versions (propriatory analysis of my own). Much simpler than the detail most commonly sought.

Just my thought, but Seisan Prime might be the inner essence of all the above.