Besides cards and numbers, what else can PAO encode?

Anything reducible to your number/card items — binary (via conversion), dates, phone numbers, PINs, IDs.

If you can map information onto your existing PAO set, PAO can carry it:

• Binary — convert bits to decimal, then use the number PAO.
• Dates / years — encode the digits.
• Phone numbers, PINs, account numbers — chunk and encode as numbers.

You don't build a new system per task; you funnel everything through the one PAO you already drilled. Reuse is the point.

Go deeper:

• Mnemonic major system (Wikipedia) — how dates, PINs and phone numbers reduce to the same sounds-to-images path.