It's kinda weird, cause the dcu probably have a different version, but the DCP below to BPLs which also again have a different version.
The DCP are needed to build the BPL files if they have other package dependencies.
Explained here:
https://sergworks.wordpress.com/2018/08/30/on-the-delphi-dcp-files/
To some degree... this should be explained more thoroughly and more official in official documentation, not third party documents.
Documentation should explain clearly:
What are DCP for ? Why are they needed ? Can they be thrown away ? And so forth.
Bye,
Skybuck.