Not sure.
I have no idea when this happened, if it happened with iOS 11, 12 or 13, but I have noticed that iPadOS is NOT reported the correct internal storage amounts.
I have no idea when this discrepancy in calculation happened, but clearly users are being told by the iOS/iPadOS system they have more internal storage than the device actually has.
The amount of available, practical, usable storage is based not only on how much iOS/iPadOS takes up but on the actual size that 1.0 GB is equivalent to, which for Apple 1.0 GB=1.074 GBs
Also, iOS/iPadOS devices need to maintain a minimum constant of between 2-4 GBs to ensure nominal, expected performance and function of iOS/iPadOS.
Also, my installation of iPadOS 13.2.3, currently, takes up 5.2 GBs of my storage
So,
After initial formatting, 64 GBs storage iPad starts out with 59.6 GBs. Minus 5-6 GBs for iOS leaves approx between 53-54 GBs. Minus 3 GBs for iOS iPadOS system reserve equals between 50-51 GBs of usable data storage space.
Even if your iPad has used 41 GBs out of the usable 51 GBs of total, usuable stirage space of your 64 GBs storage iPad, this should leave 10 GBs of internal storage.
So, your 7-8 is probably closer to the correct amount of storage, but there is still a 2-3 GBs data storage discepency.
How much space is iOS/iPadOS taking up on your iPad?
At this point it is what it is.
If you need to free up free data storage space on an iPad/iDevice, you need to start by backing up your iPad to either Apple's iCloud or by connecting your iDevice to a computer running the latest iTunes and/or some other offsite, “cloud” data storage/backup services, like Google Drive/Photos, DropBox, BOX, Amazon Cloud Drive, Flickr ( for photos/images ), etc.
Then, delete any installed apps that you no longer use or use infrequently enough that they aren't missed (you can always reinstalled any purchased or free apps at some time later, as you need them).
Then, thin out/delete any music/videos/movies/TV shows/screen recordings/images/eBooks/
eMagazine/iBooks/audio books/Documents/PDFs, etc.
If you use a POP email account on your iPad, delete/thin out any old saved emails that maybe saved to your iPad.
To permanently delete photos/images off of your iDevice go into the Photos app and find the Recently Deleted folder/album and permanently delete any photos/images stored in that folder/album.
Also, you can check to see what stuff is eating up all your valuable data storage space by going into the Settings App,,General Settings Panel, in the right hand column, tap Storage & iCloud usage panel ( in iOS 11, it’s iPad Storage ), in the top Storage Panel, tap the Manage Storage panel, wait for a list of apps to generate that will tell you how much space each app is taking up on your iDevice.
Then, do a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.
iDevices need to maintain, at the very least, a minimum of between 2-3 GBs of free data storage space, AT ALL TIMES, to insure normal/nominal functionalities/operation and general overall performance of any iDevice.
Good Luck to You!