Case Quantity in OBLPN and Current Quantity in Cases

In the OBLPN UI when we pack the OBLPN system is showing the Case Quantity value. We assume this value is getting from Item UI→ Standard Case attributes fields. But in most of the cases in our instance we did not load the value but still system is showing the correct value; we would like to know what other sources the value is getting populated?

Also, we have integration with OTM and while sending actual shipment information we would like to use filed Current Qty in Cases. Is there is any WMS API which can give this information? From the UI screen I could see this is value is getting calculated order quantity / case quantity field.