Hi Sudesh,
I also had to fight with the packaging data transferred to GTS. On top, in our process, when we create the customs document, the delivery is not yet packed or better said no packaging data is available in the delivery yet.
So, as you said, package type is mapped even in your system. But one step before that, in GTS it´s defined what type of package the mapped package type is. This you can find in the customs code list. "SPRO > Global Trade Services > Customs Management > Customs Code Lists > Maintain Customs Code Lists for Legal Regulation". There choose your legal regulation and afterwards the Customs Code Lists "PGETY Package Type". Here you can see of what type your GTS package type is. NE for example is by standard package category "2 Sales Packaging/Not packed". Based on this category you can afterwards assign this code to either a packaging material type (used in the packaging functionality in the delivery, SPRO > Global Trade Services > Customs Management > Customs Code Lists > Assignment of Packaging Material Types from Feeder Systems) or to assign this code to a sales unit measure (SPRO > Global Trade Services > Customs Management > Customs Code Lists > Derive Package Type from Sales Unit).
The second assignment is used, if your delivery is not packed and GTS derives the package type directly from the sales unit. And now, that answers your last question. As your delivery is not packed, GTS picks the sales unit and maps it and also takes the total item quantity in GTS package data.
Hope that helps a bit and it´s not too confusing.
Tobias