I am not a historian. However, let me attempt to resolve Ranjit singh puzzle of being Sansi or Jat. Let us start with what Sansi are;
http://en.wikipedia.org/wiki/Sansi_people
As per above link they were nomadic tribe who were expelled by Muslim invaders from Rajasthan. This raises many questions in one's mind;
1. Why were they expelled ? or they just retreated like many armies do in wars?
2. Expelled or retreating forces can never be of any uniform composition.
3. Why were they called Sansi ? Were they called Sansi before being expelled or after the expulsion?
4. Is word Sansi a shorter form of some other longer and difficult sound word?
Let us try to address each question one by one;
1. Sansis would not have been expelled or retreated unless they were part of a fighting force or the army of some sort of ruler. Since they were expelled by Islamic army, it would be natural to assume that they will always remain revengeful towards Muslim rulers.
2. By all logic they were part of some army and therefore they could never have been from lower sections of Hindu society.
3. In my view word Sansi must be a shorter form of kings army who fought the Muslim ruler who expelled them from Rajasthan. My best guess would be that it was called "Sansi Army" of some Sansanwal jat ruler. ... (pure wild guess friends.. will try to find proof if I can).
4. Once expelled, the best vocation for such people is to attack and loot rich people or local agents of rulers. As we know, "Chor Chor Musrere Bhai", more looters must have joined their ranks with time.
As of now, I will leave it here. I will try to research and add on to my arguments.
RK^2