嘿嘿!
I think with CD-R, when you erase a file, it is not physically erased. You just can't read it like you used to be able to. It still take up the same space.
The physical remove of the data only happens when you format that disc (not the quick erase.)
Therefore, if you format your disc and copy the three files on it, both PC and Mac would be able to read correctly...I think.