It's very easy to explain and often done...
You buy Powerflex front wishbone front bush, PFF85-601.
If you have OEM front wishbone rear bush trashed, there is no point in buying Powerflex PFF85-602 because as it is an insert for the OEM it only makes sense working in a new and untrashed bush.
The solution here, is to buy the Cupra one.
If you bought a new
ibiza, and want to prevent the front whishbone rear bush from become trashed, install the Powerflex PFF85-602 with them still new.