After the market closes at 3.30, there is a final candlestick data added (As per my understanding as the market closes , the execution engine still has few trades to execute , so it reports that data after the 3.30 pm tick).
I wan't to know how much significance you give to this data ? On daily chart it adds a quite significance sometime to nature of candelstick especially if there is breakout or breakdown etc.
Refer to 15 min nifty today's chart above , Somehow tradingview doesn't show that data on 15 min chart , but the daily chart data has that value incorporated .