Among the comments on a previous post on these topics, the Vajracchedikāprajñāpāramitā (henceforth VPP) has often been referred to. This is a very ancient Mahāyāna text, possibly even predating the Aṣṭasāhasrikā (which was the main focus of the same post). I had a look at the electronical text of the VPP and found out many seemingly contradictory statements, having more or less this form:
What is called by the Bodhisattva to be X, that the Bodhisattva calls non-X. Hence it is said to be X.This formula also applies to the perfection of knowledge (prajñāpāramitā) itself:
yaiva […] prajñāpāramitā tathāgatena bhāṣitā, saiva apāramitā tathāgatena bhāṣitā. tenocyate prajñāpāramitā
That very thing which is called perfection of knowledge by the Bodhisattva, that is called "non-perfection" by the Bodhisattva. Hence, it is said "perfection of knowledge".
Could this mean that it can only be a perfection of knowledge in the ultimate sense, if it were not one in the conventional sense? Hence:
That thing which is called perfection of knowledge by the Bodhisattva, that is called by the Bodhisattva "non [conventional] perfection. For this reason it is said to be a perfection of knowledge.
I.e., only insofar as it is distant from any conventional so-called perfections, can it be said to be one by the Bodhisattva, from the point of view of ultimate reality.
Once again, I am extremely grateful to the readers who richly commented on my previous post on Mahāyāna texts expressing paradoxes. You might also be interested in its "sequel".