@NickSuite you need to sum up the quantity of all posting transactions from inventory GL account for that item up until that date.

Which GL accounts should I use? Isn't it better to use the transactions such as IR, IA, IT?

You can check the GL impact of existing transactions. I actually recently came across a lengthy article explaining the pitfalls of using transaction type instead of gl account. http://blog.prolecto.com/2019/10/19/learn-how-to-craft-better-netsuite-financial-saved-searches/

Thank you for the article. I will go with the accounts. I believe COGS will do the trick.