Holdings showing doubt

Though my holdings are from NSE , but zerodha showing its from BSE. I already heard one reason, that zerodha is showing the depository which has high price… NSE has higher price but it’s still always showing BSE and somedays show NSE . There is no fixed system I guess.
It’s making an issue to create gtt orders and overall pnl watching. Everytime I need to double check with NSE price. What is the logic behind this ?

It would be easier to see from where we bought it …from a buyer’s perspective

I do buy the same stock from both the exchanges as per the pricing convenience but I didn’t think of this. I will start observing this from now onwards.