Question for the grammar Nazis

[Ghoulish Delight]

As Alex said, you'll find different style guides with different answers regarding proper names. On top of that, you'll see the same style guide give a different answer depending on the name (using the "Whichever sounds better" rule).

Examples:
Most guides will have "Jesus'" rather than "Jesus's".
Jones' vs. Jones's can go either way.

It goes on. When something that's singular ends with an 's', the standard rules go out the window. There's the added gray area in this particular case because the individual word the apostrophe is being applied to is plural, but the conceptual unit it's being applied to is singular.

So in the end, it's about picking one and being consistent.