[a2tech]

Note that this is from the early days of iTunes--things could be radically different behind the scenes now.

I suspect if it isn't listed as 'Apple Lossless' or one of the other fancy labels, its probably originally from a CD rip somewhere. I know from listening to niche-y music, that music catalogs can often be wrong and will be published to multiple music sites. For example Junior Brown's album 'Junior Brown: Greatest Hits' has a track on it that is half glitches AND its the exact same on multiple services and has persisted for years even though I reported it several times on each service. There's also a sea shanty album where half the tracks are static. I reported it to iTunes and Amazon and received boilerplate responses. I then sent an email to the actual band (hard to believe, but its a bunch of old guys) and they contacted their record company...but even they couldn't get it straightened out.

[neon_electro]

Even when it lists Apple Lossless, there can still be errors in the files.

I found an album from 2001 on Apple Music recently and discovered one of the tracks cuts out at just after one minute, even though Discogs reports the track should be 4 minutes 30 seconds (Slide - Closure (Lounge-Tech Mix), on the Nu Progressive Era compilation: https://www.discogs.com/master/90383-Red-Jerry-Nu-Progressiv...). The album is listed as "Apple Lossless".

I went and bought the original CD version JUST to have that one track in full.

[astrange]

"Mastered for iTunes" is the tag that means someone actually listened to it. (Technically it means the AAC file was checked that it doesn't have more clipping after encode than before it. There's a public PDF about this out there somewhere.)

It's usually missing, but hopefully someone listened anyway.