From what little I can infer, they seem to be gearing up to reissue said material on a new sub-label called Chappell Vaults Anthologies.
hxxps://productionmusic.fandom.com/wiki/List_of_miscellaneous_Chappell_Recorded_Music_Library_CD/digital_albums#Chappell_Vaults_Anthologies
That being said, I can't fathom why this would necessitate delisting the original albums that contained this material, especially how other libraries that have reissued older material don't pull previous reissues off older albums. Not sure what the thought process was here.