Is a PAO system standard, or does everyone build their own?

Personal — you build and drill your own PAO, because the images must be vivid to you.

There's no official 52-card PAO. The people, actions and objects work only if they're instantly evocative for you — your celebrities, your associations, your in-jokes. Two people's systems look nothing alike, and that's correct: the value is in how fast you can see each image. Courses give example schemes to copy or adapt, but the system you drill into fluency should be your own.

Go deeper:

• Dominic system (Wikipedia) — a famous personal number system — evidence systems are individually built.