Dirkee is NOT on the same spawn timer as Vyragosa and TLPD. It is no more related to these 2 as any other rare in Northrend. (Andrew pointed out this wasn't on the site somehow, and Thank you sir) -- Andrew also attached this entertaining screenshot he took when he figured it out. Much more interesting than when I did, dirkee was up by engine, then vyra was engaged and killed just south of where he was long before his corpse was gone. The time I witnessed it would have been a shittier screenshot, for sure.
Regarding Linkable Reigns:
Reins do not only become linkable when somebody kills/loots Aeonaxx. There are 3 reasons (that I know of) why reigns switch from unlinkable to linkable. And 2 of the reasons are why I don't even bother with it.
1) Somebody kills TLPD and loots the reins (well known, and already stated above).
2) Someone has an old version of Atlas Loot from before Blizzard had them alter the way it retrieves information because it would force the server to fetch uncached item information - thus making anything it requested linkable. - Anyone that still has one of the versions can punch in the reigns and force them to be linkable [apparently for a short time, from what people who do it have said] (don't ask me what version number(s) do it I don't know, probably can find out on google)
3) A player has the reins unlearned in their bags/bank and logged in. Not sure if they have to mouse over it to do it or what, but this is a long known reason for things becoming linkable.
(I'm not putting up the script because I personally find it to be a moot point resulting in more self-inflicted grief than needs to be applied beyond an already probably long camp.)
Because of this, I do not suggest putting any validity in the reign linking meaning anything. Because of reasons 2 and 3. There being more reasons something becomes linkable than only being looted means it's a pretty pointless thing to exersize.
Furthermore, when I got PSD on my Druid, the reigns stopped being linkable about 45 minutes later. There was no reset, crash or maintenance. They just stopped being linkable.
Rein Link Theories
Some other theories on this that I can't really prove easily that could be plausable are if it drops on one server in a battlegroup, it could become linkable in all servers on that battlegroup. Another theory is it could be linkable if someone has it in their bags in a random and makes it linkable on everyone's server in that random.