The late raised cavalry regiments in WWI were, I believe, in response to, or in anticipation of, the troubles on the NWF which eventually led, in 1919, to a massive campaign there. Disbanded as soon as that ended as an economy.
The IA, like the BA, was very big on 'perpetuation', so re-using unit numbers made sense. The only WWII unit I've found info. on, in an admittedly brief search, was the 45th, which was made up of Sikhs and Pathans, apparently pulled from other units, and which saw service in Burma. There were certainly more trained tankers than there were tanks and armoured cars, so I suspect that these 'new' units may have tried to use cadres from existing units - a few experienced men leavening drafts of particularly apt recruits to quickly create units which could arguably by used in action at once. The relative rarity of tanks and tank actions in India/Burma may also explain why some were disbanded again before 1945.
All this, perhaps needless to say, is semi-informed musing and should be taken as such.