I've read through four of Paasch's five posts. Some comments.
In Scotus: haecceities must be some positive entity he introduces Scotus' notion of haecceity: some presumed feature of an object that makes it the individual thing it is, different from any other individual. Paasch notes Scotus' rejection of the theory that individuals are individuated by a unique set of incidental features (a theory which was in some way comparable to the description theory of proper names rejected by Kripke in the 1970's). In What are haecceities? he wonders about the difference between 'haecceity' or thisness, and 'quiddity' or whatness. Thisness is the 'unrepeatability' of a feature. A qualitative or 'what kind of' feature is essentially repeatable. If you can have one man or giraffe, you can have as many men or giraffes as you like. Thisness is not repeatable. He asks "why couldn't God create an identical copy of a haecceity? What makes it so unrepeatable?".
In What makes a haecceity unrepeatable? he argues that God can do anything that does not involve a contradiction [correct - a standard medieval assumption, denied by only a few such as Peter Damian, possibly]. Then he introduces the idea of a reference relation or identity relation, arguing that only by the assumption of such a relation can we explain why the repeating 'thisness' would involve contradiction. Suppose the haecceity, the 'being this person' of Socrates involves the feature 'being identical with Socrates', call this Socrateity. And suppose God tried to clone another individual who also had Socrateity. But any individual with Socrateity has the feature being-identical-with-Socrates. Another individual would (from the definition of 'another') be non-identical. "One might take this example and generalize: the only way that cloning a thisness will result in a contradiction is if the thisness involves some sort of intrinsic reference to the individual in question".
I don't quite see why the generalisation follows. His argument shows that a relation of such a sort guarantees unrepeatability, not that only such a relation will do this. But let's move to his final post. In Are Scotus's haecceities really unrepeatable? he gives two arguments.
1. The identity relation (by which I assume he means the relation between some thisness, e.g. Socrateity, and any individual that instantiates it) is a relation, but Scotus argues that thisnesses are absolute (non-relational) entities. (Actually I'm not sure whether Scotus argues this. He only explicitly mentions relation - relatio, respectivum - twice in distinction III. But I am far from comprehending Scotus). But if haecceity is an absolute entity, why couldn't God clone it, or rather, clone an individual having the same haecceity.
2. Scotus believes that a relation 'supervenes on' the things they relate, and is thus posterior to the things it relates. If haecceity involves a relation between the haecceity and the individual it individuates, then the individual is already individuated. Relationships "cannot do any individuating, for they show up on the scene too late, as it were, to do any individuating". Actually this objection (according to Peter King) derives from Abelard*. The individuality of an individual cannot derive from or be dependent on the individual himself.
In summary: if haecceity is a relation, it involves a relation with the individual, thus is posterior to the individuals existence, thus cannot explain its individuality. If it is an absolute entity, why can't it be repeatable?
I have no answer to this right now (I am merely summarising four long posts by Paasch). I am wondering whether Scotus can be defended at all, or whether he can be defended using his idea that individuation is a sort of indivisibility (for that is what individuum actually means), and that it involves what Scotus calls the 'repugnance' of an individual to further division. Et ita natura speciei specialissimae non est de se haec, sicut nec aliquid divisibile ex natura sua est de se hoc, ita quod repugnet sibi de se dividi in partes, quia tunc non posset recipere aliquid per quod formaliter competeret sibi talis divisio. "And so the nature of the most specific species is not of itself this, just as something divisible is not from its nature of itself this, so that it is of itself repugnant to it to be divided into parts, because then it could not receive something through which formally such division would belong to it".
* Logica Ingredientibus 1.01 n26, cited in Peter King, "The Problem of Individuation in the Middle Ages", Theoria 66 (2000), 159-184, preprint here.