Ah, yes, if you uninstalled the app that might have been terminal for the data on your device!
The instances folder will have a series of folders, one for each completed form (submission) - in each folder will be a.xml file and any media - if those folders are empty, you have no data.
So, on to the other 3 devices....
The data is stored in the instances folder and they don't 'go anywhere' unless you delete them from the device. If the tablets have not been set up with a Central or Kobo server connection then there is nowhere to send the submissions. But don't try out of curiosity until you've got it on your hard drive!
The instructions for briefcase should see you through. But just for clarity (and to include what I forgot previously) here is an example:
Create a folder on your PC, maybe called ODK.
Navigate to the uuid folder on the first tablet
You should see folders called forms AND instances (among others)
Copy BOTH of these to the folder ODK on your PC
Open ODK Briefcase and if you haven't already, select a (DIFFERENT) folder as the 'storage location' (under 'settings')- this will create a new folder on your PC called Briefcase Storage (with subfolders when you pull data)
On the 'Pull' menu, use the dropdown and select 'Collect Directory' and navigate to the ODK folder you created in step 1 - that will read the form definitions that are in the forms folder.
You should see the form listed, so select that and click 'Pull' (that basically copies everything to the Briefcase Storage folder you just created)
On the EXPORT menu you can then configure what to export and where...
It's been a while since I used Briefcase but it was my only way of transferring data for years and it's easy to use once you get the hang of it - pull the data from the ODK folder, Briefcase creates a copy of everything, then export to csv (and you get a 3rd copy of any images!) - the configuration of EXPORT is important as you might NOT want to overwrite existing files (in the destination folder), given how precious your data is.
When you are doing the next round of data collection I recommend that you use a server for submissions - Central is very robust (you can host your own) but other flavours are available.
Hope this helps...