Marqeta's platform can only receive events for cards that are issued by us. There is no functionality today to enroll external cards onto our platform on an ad-hoc basis, and thereby allow you to see the events on those cards. This is mostly due to the way that card event routing works at the Networks (Visa, Mastercard, etc.). When a card is first created, the first 6 digits of the card number is a static prefix like: 412345. The networks maintains a mapping so that they know that 412345 maps to Bank X, and not Bank Y.
If that mapping needed to change, it involves a lengthy process that would re-map the entire range of cards (every card beginning with '412345'), not just a single card. This is called a 'BIN migration' and is the only mechanism that I'm aware of to transfer ownership of a BIN range from one issuing bank/processor to another.
Therefore, I'm not sure it would be possible to accomplish this type of card enrollment without some additional functionality being built out by the networks. Something to keep an eye out for perhaps!
Hopefully this helps - let us know if you have any other questions!