There is a substantial specialist literature on the history of numerals, from Smith and Karpinski (1911) and Florian Cajori (1929) through to Georges Ifrah, Victor Katz and Charles Burnett (2006).  Some of this has been mentioned in this forum before, I believe.  It would be best to refer to that literature before posting further notes on the topic.  The most pertinent parts of this literature for India have been cited and discussed by Kim Plofker in her 2009 book Mathematics in India, especially chapter 3.

Best,
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Dr Dominik Wujastyk