In 8.2 there were changes with JS files, more specifically the jquery library and how you can reference it. There is an article here. Adding the stylesheets and jquery librarys as a whole did not change, the functionality is still the same, just how your reference the jquery object ($).
When comparing your databaes and seeing a smaller number of records, what tables were you seeing this in? Is your data missing? There are several database and API changes which will affect the number of records and actual data as Kentico works towards new features and removing old, non-used features and optimizes the system. Unless your data is missing, I wouldn't be concerned.
In order to use your old database (v8.0.21) you would also need to roll back the code base for the website to that version as well. My question back to you is did you run the website each time after the upgrade? If not, this WILL cause problems.