Determine tracks added from subscription

[jdheyburn]

I currently have a GPM subscription alongside thousands of tracks that I've uploaded and I want to use gmusicapi to tell me what tracks I've uploaded vs what have been added from the subscription.

I've pulled out a diff of the keys in a track that I uploaded vs a track that I added via subscription.

Fields in added_track not in uploaded_track
trackType
explicitType

trackType has a numeric value of either 4 or 8.
explicitType has a numeric value of either 1, 2, or 3.

Whenever there is trackType, there will be explicitType. However I have come across some tracks that have only explicitType from this pair. For these that only have explicitType, they look to be songs that I purchased from iTunes Music back in the day.

1. Do you know the significance of these fields (trackType and explicitType)?
2. Can these be used to accurately determine a track added from a subscription? From my investigation it seems so.
3. I am thinking of adding a PR to include a function to report on tracks added from a subscription - thoughts?

I myself am migrating away from GPM so I want to know what tracks to add to my new streaming platform. Others might find this beneficial too - it could be used in a migrating tool from one platform to another.