it would really be on a case by case basis as to what the deals were with the producer/writer. If they were paid, then yes, it’s likely Parlophone would own the rights, if they were working on the basis that Parlophone would pay for anything they wanted to use, the writer/producer would own the rights.
I guess that’s why Red One would (apparently) have been able to delete his tracks with her.
Kylie will own the rights to all of her material within the next 5 years from what I understand, so it will be interesting to see if she approves of retrospective releases. Something like Pet Shop Boys Further Listening releases would be incredible.