Metadata lives inside the file, not next to it
Audio metadata (title, artist, album, track number, cover art) is embedded directly inside the audio file itself as tags, not stored in a separate sidecar file or derived from the filename — which is exactly why the same MP3 can show completely different, correct information in every music player it's opened in, regardless of what the file is actually named. Renaming a file doesn't touch its tags, and correcting its tags doesn't require renaming the file.
This also explains why two identically-named files can display totally different track info, and why a poorly-tagged file stays poorly labeled no matter how many times you rename it — the fix has to happen at the tag level, not the filename level.
Why a whole album can end up scattered or out of order
Music library apps typically sort and group tracks using the album and track-number tags, not the file order on disk — if those tags are missing, inconsistent, or wrong (a common result of ripping CDs with imperfect software, or downloading from sources with inconsistent tagging), tracks from the same album can scatter into the wrong order or even appear as separate, unrelated albums. Fixing the album and track-number tags to be consistent across every track is what pulls a scattered album back into a single, correctly-ordered listing.
Cover art is a tag too, not a folder image
Album art displayed by most modern music players and phones is typically embedded directly in the file's metadata as image data, rather than read from a separate cover.jpg sitting in the same folder — which is why a file can play with no artwork even when a correctly-named image file sits right next to it. Embedding the artwork directly into the file's tags is what makes it travel with the file wherever it's copied or synced.
Batch editing saves the tedium of an entire album
For a full album with a dozen or more tracks, editing tags one file at a time is tedious and error-prone — batch tools that let you set the shared fields (artist, album, year, genre, cover art) once across every selected file, while auto-incrementing just the track number, turn what would be dozens of repetitive edits into a single pass.