Actually my thoughts were going a different way: if one Man Singh could be recorded as Mānasāhi, this same phenomenon could have occurred in the case of other Man Singhs.
However, if I am not wrong, there have been more than one Man Singh in Northern India (for certain reasons I am inclined not too consider Nepal, although for the moment I can't rule out that this king was from Nepal), so one does not know exactly where to start digging.