That timeline does not contradict my point, if anything it reinforces it, as follows.
SD elected to switch at the end of Feb.2010, as you say. But with the Qualifiers having been completed by the end of 2009 (Nov?), FIFA anticipated a number of new registrations and applications to switch before the Finals. (Quite obviously they needed to be satisfied that all players appearing were properly eligible and registered.)
Consequently they put a hold on effecting all non-essential registrations, inc SD's, until after the backlog was cleared and the tournament was out of the way (Final was mid-July). Which will have been why it took until 20 August for them to get round to SD's application, amongst all the rest. (This will have cleared the decks for European competitions starting in the autumn)
Meanwhile, Kearns/CAS was nothing whatever to do with it, since SD's Donegal Da meant that the IFA did not contest SD's switch at any stage. Therefore they had no cause to delay his registration. Indeed, even if they had been so inclined for some reason, I'm pretty sure there will have been no competitive matches at any age group coming up that the ROI might have needed SD for, because it was approaching the season's end.
Therefore what would have been the point of withholding his documents, since the FAI could, of course, have gone ahead regardless and picked him for any friendlies they had planned whilst they waited on the IFA?