AppleMusic/iTunes ripped CDs can contain a tag: ‘ itunes_cddb_1’ that includes sector
information from the physical CD rip.
 
A  MusicBrainz DISCID can be constructed from this information.
 
The DISCID can then be used by Picard for looking up the release in the MB database.
This can produce a much more targeted result than other lookup methods.
 
If Picard detects this tag it should offer a DISCID lookup method in addition to the others.
 
EG. 
 
itunes_cddb_1 : A70A440C+197277+12+150+14997+30287+51760+65322+80577+94467+109880+127055+144497+159062+179827
 
12 - # of tracks
150+14997…179827 - 12 track sector starts
197277 - final track end
 
The sectors numbers are biased by 150.
 
I have used these values to create a fake rip log that Picard then turns into a DISCID
but have not computed the DISCID myself. 
 
For this example: (there were four possible matches)
MusicBrainz Disc Id: NA_4BU9DZbH8ZER2EWjKp_epSXY-
MusicBrainz Release Id: ebca62ba-87f5-42f6-a50e-ef1e153eae0d
 
For the format, here are three other random examples from my collection:
9D0AA60D+204632+13+150+13367+26762+41472+56677+77757+87752+105782+121392+136765+152182+166200+179490
6B10B619+321046+25+150+4587+16915+25177+34329+45963+61306+74765+85721+101372+112219+129149+141120+155940+168502+178320+186577+198229+229876+239926+253896+264727+278748+302507+320279
110B2702+214306+2+150+137478
 
-
 
Looking at my collection, it looks like Apple started including this tag with iTunes version 10, which is around 2010.
 
Apple Music (the iTunes replacement) can rip to several formats. Both AAC & ALAC are stored in an mp4 container and they include this tag. Other output formats, notably mp3 do not.