You don’t have to use the PAO format for everything. PAO is a particular way of organizing imagery, but with the Major System as a foundation you can get creative outside of that structure as well. For something thats not going to change, like a credit card number, you have the option to take your time and craft your mnemonic imagery to include longer or different words than you have in your pre-defined 2-digit system.
1213 could be “TaNDeM” like a skydiver duo. Or “DowNTiMe” where someone’s killing time at the office water cooler…
For Dates, having some kind of indicator for centuries is a good idea, but it doesn’t have to be a P or A or O. It could be an adjective, a “texture” or “filter” over your scene, or you can create specific memory palace areas that represent different centuries and set your scenes there. You could also use 3-digit object to represent the last 3 digits of the date. This wouldn’t require you to necessarily memorize a 3-digit list, since the application isn’t speed competetition. You could use a resource like memcoder.com to give you ideas for those 3-digit numbers. (Or take a look around the forum for some lists. Here’s mine: New Two-Card System: 2-block (1352 element), Simple Phonetic Structure - #25 by TheHumanTim )
1934 would be 934… BoMbeR or BeaMeR or PalMeR could be that image.
Again, if you’re trying to memorize random number sequences as fast as possible a pre-defined system like PAO is great, but explore other applications of major if you aren’t in a rush to encode these longer or odd length strings.