By default, Amazon has a setting turned on in a Seller's account to use the manufacturer barcode for their items. This is also known as Stickerless Commingling. For items that are eligible, you can send them into Amazon without having to label them. However, if they are not eligible, they will have to be Seller Labeled. Since Amazon prevents us third party software providers from combining differing label types into the same shipments, we have to split the NO_LABEL or commingled items into their own shipment.
To turn off Stickerless, Commingled Inventory if you would like:
Seller Central->Settings->Fulfillment by Amazon:
Scroll down to FBA Product Barcode Preference and click the Edit button to the far right
Select Amazon barcode and click Update
Note: Any changes you make to this setting immediately takes effect in the same batch.
If your settings are NO_LABEL when you add your first item to a batch, you will be notified and prompted to change the setting if necessary.
If you choose to update your preference, you will be taken to the barcode settings page in Seller Central. Once you change the setting and return to InventoryLab, a new MSKU will be created once you choose 'Add to Batch'. If you continue as commingled, your item will add to your batch as NO_LABEL.
If you would like to combine the different label types into one shipment, you can do so but it requires uploading a shipping plan into Seller Central and creating your shipments there.
For more information on this topic, feel free to check out Amazon's Help Page.