Not sure where to put this, so I hope the mods can move it if this is the wrong spot.
I have an old reference sheet from many years ago that lists what bonus types stack. These rules are different from PF and 3.5 so I'm hoping someone can tell me where they came from. They might come from some d20 spin off but I dont have access to my old pdfs to check.
The differences from PF are,
Competence bonuses, all items stack but with only one spell,
Deflection, insight, and luck stack with themselves
And shield bonuses stack 1 mundane bonus plus 1 spell, plus half of any further spells.
Anyone know where these odd rules come from?
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Dodge bonuses stack.
The magic on a suit of armor or a shield, for example: +1 chain shirt, is an enhancement bonus, but not an enhancement bonus to you, rather an enhancement bonus to the armor bonus that shield or armor provides.
The general rule is that bonuses of the same /type/ do not stack with one another. So, you could not use both a Shield spell and a +2 heavy wood shield to get +8 to your armor class. Only one or the other would apply. Even the spell and a mundane heavy shield is only +4 armor class from the spell.
Those may be from way back in the 3.0 days, before they started streamlining. I never played 3.5, so I can't comment there.
In short answer is if the bonus is of the same type they usually don't stack i.e. If you get two shield bonuses only the higher of the two is effective.
I think what you're looking for is in the glossary here. . If you look at the entries for 'Bonus...' each one will tell you if they stack or not.
Also, the quote below is from the PFSRD Stacking magic effects.
Stacking Effects (spells)
Spells that provide bonuses or penalties on attack rolls, damage rolls, saving throws, and other attributes usually do not stack with themselves. More generally, two bonuses of the same type don't stack even if they come from different spells (or from effects other than spells; see Bonus Types, above).
Different Bonus Types
The bonuses or penalties from two different spells stack if the modifiers are of different types. A bonus that doesn't have a type stacks with any bonus.
Same Effect More than Once in Different Strengths
In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the one with the highest strength applies.
Same Effect with Differing Results
The same spell can sometimes produce varying effects if applied to the same recipient more than once. Usually the last spell in the series trumps the others. None of the previous spells are actually removed or dispelled, but their effects become irrelevant while the final spell in the series lasts.
One Effect Makes Another Irrelevant
Sometimes, one spell can render a later spell irrelevant. Both spells are still active, but one has rendered the other useless in some fashion.
Multiple Mental Control Effects
Sometimes magical effects that establish mental control render each other irrelevant, such as spells that remove the subject's ability to act. Mental controls that don't remove the recipient's ability to act usually do not interfere with each other. If a creature is under the mental control of two or more creatures, it tends to obey each to the best of its ability, and to the extent of the control each effect allows. If the controlled creature receives conflicting orders simultaneously, the competing controllers must make opposed Charisma checks to determine which one the creature obeys.
Spells with Opposite Effects
Spells with opposite effects apply normally, with all bonuses, penalties, or changes accruing in the order that they apply. Some spells negate or counter each other. This is a special effect that is noted in a spell's description.
Instantaneous Effects
Two or more spells with instantaneous durations work cumulatively when they affect the same target.
I have been able to verify by the books that these dont come from 3.0, 3.5, or PF. (Unless perhaps it was changed with errata from earlier printings of 3.0)
@ Speaker forthe dead
I know what PF is now, what Im looking for is where these rules came from, so I know where where to file it for whenever I get a computer to access my old files again, and to solve my curiousity.
I'm not sure about the origin of your list. Some of them sound correct, the rest might be old house rules.