When applying multiple templates, are they applied concurrently or consecutively?

Question

Pathfinder is pretty clear about the ability to stack templates, as there are multiple published examples of such. At issue is that some templates would seem mutually exclusive if templates are applied consecutively; for example, both Skeleton and Skeletal Champion are "an acquired template that can be added to any corporeal creature (other than an undead) that has a skeletal system".

Would it be possible for a spell caster (or pair of spell casters) to impart both the Bloody variant or Burning variant Skeleton template and the Skeletal Champion template onto the same corpse to yield a Bloody Skeletal Champion? Mechanically, if allowed, simultaneity of animate dead and create undead (the spells used in creating these templates) could be achieved by readied actions or contingency spells — so that's not an issue. The issue is entirely that consecutive application would yield a creature of a type invalid for the second template.

Answer 1

In 3.5, Templates are always applied consecutively:

Adding More Than One Template

In theory, there’s no limit to the number of templates you can add to a creature. To add more than one template, just apply each template one at a time. Always apply inherited templates before applying acquired templates. Whenever you add multiple templates, pay attention to the creature’s type—you may add a template that makes the creature ineligible for other templates you might want to add.

(from Improving Monsters)

Pathfinder, however, occludes the templating section in its advice on monster improvement. This means that, while the developers presumably still intend templates to be applied one-at-a-time, no rule indicating that actually exists in Pathfinder. Thusly, the answer is not specified by the rules, as written.

Since simultaneous application is not possible in the general case, however¹, not disallowing simultaneous templating will lead to seriously problematic undefined behavior (though not during game sessions).

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1. That is, one cannot apply two templates simultaneously while conforming to the rules for applying templates, in general. You can do it in the special case where for each step either one template does nothing or both templates agree exactly on what must be done. This is because you apply templates in a step-by-step fashion and any conflict between instructions within a template would be unresolvable within the rules-as-written. For example, a prospective burning skeletal champion loses and gains immunity to cold simultaneously, and there's no clear end-state for its immunities as a result.

Answer 2

In the 3rd printing of Pathfinder RPG Bestiary, on page 251 under "variant skeletons," the text explicitly says:

Each of the following skeleton types modifies the base skeleton in a few key ways. Except as noted, these variations can be stacked with one another—it’s possible to have a bloody burning skeletal champion.

So to answer my own question for the first time: at least for the variant skeleton templates, they explicitly stack. It should be noted that while this specific rule conclusively answers the example given to illustrate the question, the underlying question is about the general rule for stacking templates — and remains unanswered.