So. Pathfinder Chronicler is basically "meant" to stack with your bard level for the purpose of determining your bardic performance rounds per day.
The relevant rules text of Pathfinder Chronicler, however, says it stacks with levels in any other class that grants a similar ability:
Bardic Knowledge (Ex): This ability is identical to the bard class feature of the same name, and levels in this class stack with levels in any other class that grants a similar ability.
Bardic Performance (Su): At 3rd level, a Pathfinder chronicler gains this ability, which functions like the bard class feature of the same name, except that the chronicler's effective bard level is 2 lower than her class level. Levels in this class stack with levels in any other class that grants a similar ability to determine her effective bard level.
The question, then, is how it stacks, especially when considering multiclassed Bard/PFC/X/Y, or X/Y/PFC, where X or Y may themselves have the language of the Pathfinder Chronicler's stacking effect, and what is similar enough to stack with.
At time of writing I'm pretty sure I've found all the things that actually grant bardic performances, but it's possible I'm missing something.
Levels in Bard: So obvious that we do not need to consider them except as the base case from which others diverge.
Levels in Skald: Answered here, though not necessarily for all interactions.
Sensei Monk: "A sensei’s advice is identical to bardic performance (using oratory), [...] as a bard of the sensei’s level,"
Argent Performance: An argent dramaturge can use Perform (sing) to create special magical effects that hinder outsiders (particularly those affected by silver, such as devils) as per the bardic performance bard class feature. She can use this ability for 2 rounds per day for each argent dramaturge level she has, and can use rounds of bardic performance gained from bard levels to perform argent performances and vice-versa.
A sphere singer is able to use Perform (sing) to create magical effects, as per the bardic performance bard class feature.
Inspiring Command (Ex): A battle herald uses her keen tactical acumen and decisive judgment to lead others to victory, as well as her mastery of command to assist herself and her allies in battle. All battle heralds may use inspiring command to inspire courage (as the bardic performance ability); bard and battle herald levels stack to determine the bonuses provided by inspire courage.
Oath of the People's Council Paladin: "This functions as bardic performance as per a bard of her paladin level using Perform (oratory)."
Carnivalist Rogue: Levels stack with "Levels in a class with the distraction or fascinate bardic performances [...] for the purpose of determining bonuses granted by these performances." (This interaction is probably a question in and of itself, really.)
Evangelist Cleric: "This ability is similar in all respects to bardic performance as used by a bard of the same level (including interactions with feats, spells, and prestige classes), using Perform (oratory) as the evangelist’s performance skill."
Exemplar Brawler: "At 3rd level, an exemplar gains the ability to use certain bardic performances. [...] The exemplar’s effective bard level for this ability is equal to her brawler level – 2. [...] This ability otherwise functions as bardic performance; feats and other effects that affect bardic performance (such as the Extra Performance feat) apply to it."
Storyteller Medium: "This ability is similar in all respects to bardic performance as used by a bard of the storyteller’s medium level (including interactions with feats, spells, and other abilities), [...]"
Ocean's Echo Oracle "This ability is identical to bardic performance (using Perform [sing] only), [...] as a bard of the ocean’s echo’s level."
Song-Bound Oracle: "You can perform the countersong bardic performance (using Perform [sing] only) for a number of rounds per day equal to your oracle level. If you gain the bardic performance class feature, these rounds are in addition to any other bardic performance rounds you gain, but they can be used only for the countersong bardic performance."
So. How do they stack, if they do, and why do or don't they stack? I am primarily interested in Pathfinder Chronicler, but I believe that Carnivalist Rogue is also worth special attention.
There is also the question of whether Pathfinder Chronicler stacks twice via Evangelist (or any other PrC with the "aligned class" feature, whether aligned to the base Bard or at PFC itself), or the Loremaster PrC's "this stacks with Bardic Knowledge" bonus to Knowledge checks, but those are stretching the scope of this question a bit.
For characters taking multiclass levels in X/Y/Pathfinder Chronicler/(potentially) Z,
- How do you determine which performances they can access?
- What is their total net bonus to knowledge checks/how is that determined?
- How many rounds of performance/performance-alikes would they have, and would those rounds be interchangeable or not in the general case (i.e. using the language "as a bard")? What about the other bard prestiges (e.g. Argent Dramaturge, which honestly I can answer 'only if you're a bard' myself for)?
- Are there notable exceptions to the general case in which something stacks that would not otherwise?