CD-R and DVD-R/DVD+R do finalize when completed and ejected although there may be programs that can treat them as if they are RW type, haven't needed to try that.
As for the type of data, if it plays in a CD player the files most likely will show on the disc as .cda which are very small and only pointers to the hidden data on the disc which I think are actually .wma format. I've Ripped my audio CDs to .mp3 format for playing on the little MP3 Players such as an iPod and other brands.
Data discs can hold many types of files for storage such as Office documents, movies/videos, pictures, etc., and can be accessed by programs that created them but usually can't change them. When discs are finalized they can't be changed, become ROM/Read Only Memory.
The discs can be viewed in File Explorer to determine what they are, name and extension.