Are XP award for one large encounter vs. lots of smaller encounters different?

Question

Suppose my five level-2 player characters (PCs) face 10 CR2 challenges/encounters in a given Pathfinder session. To be concrete, let's assume these encounters are monsters that are each worth 500 XP. I could send these monsters at the party individually or en masse....

Case 1: Individual Encounters

The PCs face each of these monsters in separate encounters separated by a significant amount of time (>20 minutes each). Each encounter is relatively easy on its own because the five PCs can easily gang up on a single monster, so the PCs defeat each monster with ease.

Case 2: A Single Massive Encounter

The PCs face all of these monsters at the same time. They are severely tested and nearly die, but they manage to survive.

My Question

If the party defeats 10 monsters worth 500 XP each, the party would earn a total of 5000 XP, or 1000 XP/PC. In Case 1, they expend little effort/resources to do so. In Case 2, they use much more resources and the whole encounter is far more difficult. It would seem that they should earn more XP for Case 2 than in Case 1. (Then again, perhaps the PCs were clever and somehow planned to face the monsters individually, so perhaps their planning should be rewarded with easy XP.)

Are there any rules/suggestions in core Pathfinder which help account for this? For example, in 5e, there are evidently "Encounter XP Multipliers" when the party encounters a bunch of monsters in a group which change the "effective CR" of an encounter (c.f. this question). I seem to vaguely remember 3.5e having something similar, where the "effective CR" would be different. Does Pathfinder has a way to do this?

Disclaimer: I acknowledge that GMs award XP in different ways. Some would add up the XP from each encounter/monster, some would calculate XP based on an "effective CR", others might award XP based on their own estimate of the difficulty, and still others have their own approach. I'm looking for core rules (preferably) or published 3rd party rules.

Epilogue

This situation happened a day or two before I posted this question. My players entered a spider-lair cave with spiders, bat swarms, pit traps (with bodies and minor loot), cave fishers, and similar challenges. They had something like 8-10 such encounters, plus a few others I'm not counting. They used a torch to light the spider web on fire, which spread throughout the cave, dissipated the bats, killed several spiders deeper in the cave, and so on. The pits were not deadly (though they hurt), and after the second one, they decided to creep through the cave very carefully, specifically looking for pits to avoid. When they found one, they hopped into it looking for loot. Thus they "defeated" a half-dozen pit traps -- as well as the spiders and bats -- super-effectively. They earned more XP in this session (calculated normally) than they had in the three prior sessions combined. I felt really bad giving them so much XP because one of the PCs was absent (house rule: absent players don't get XP for sessions they miss).

Answer 1

There are no rules for increasing the XP for an individual monster based on the number of allies it had in the battle.

However, there are clear rules about encounter difficulty. The gamemastering rules tell you that you should first choose an encounter difficulty (in the case of a level-2 party, you'd choose between CR1 and CR5). From that encounter difficulty you should find your XP budget, and then you should select a number of monsters fitting into that XP budget. In the example you give, if your average party level is 2, you can't choose more than a CR5 encounter, which would be at most three of those 500xp monsters.

In other words: if you send all those monsters at the party at the same time, then it is not 10 CR2 encounters any more -- it is one CR8 encounter, and the gamemastering rules tell you that you shouldn't do that.

So, when you ask: "are there any rules/suggestions in Pathfinder that account for this?", the answer is that the rules restrict you to a narrow band of difficulty, such that the superdifficult encounters you're describing can never happen.

Answer 2

No

Pathfinder encounter difficulty is strictly calculated as a sum of the encountered creatures XP. There are not multipliers to the difficulty based on the number of creatures (which I personally prefer). It is also worth mentioning that the 5e encounter multipliers are only used to calculate difficulty and do not modify actual experience gained. You are of course welcome to award XP for whatever you please but I would discourage granting extra XP for fighting more monsters at once as it encourages that behavior (which is not particularly sound tactics).

Answer 3

Take for example 16 CR 1 encounters. This would net 6400 xp, or 1600 each for 4 members. Now take a single encounter with 16 CR 1 creatures, that's a CR 9 encounter and the same, 6400 xp. Depending on the equivalences, it may be worth less or more. Essentially, with pathfinder (or the UA Level Independent XP Awards in 3.5), the awards are the same. With DMG xp rules, the party would either earn quite a bit more, or none at all, depending on the equivalent EL compared to each party member's level. Pathfinder (and the UA awards) assume the awards are static and don't change if the party is of varied levels or different level than the encounter.

Keeping things static also keeps the wealth by level static. If you award more xp, you'll need to award more wealth or the players will fall behind in wealth.