Why does copyCard copy the UniqueNumber?

[friarsol]

Can we use UniqueNumber and Timestamp to determine Uniqueness of a card?

[Braids]

Can we use UniqueNumber and Timestamp to determine Uniqueness of a card?

in what context? for Momentary Blink?

[friarsol]

Can we use UniqueNumber and Timestamp to determine Uniqueness of a card?

in what context? for Momentary Blink?

If the worry is Unique Number growing too large during the game, accessing the Timestamp at the time of Targeting might resolve the issue.

[mtgrares]

Below is a private message from ubeefx, creator of Magarena which separates a card from its ID.

In Magarena a card has a simple id, like card number in library.
A permanent has a generated unique id and a reference to the card it represents.
So card and permanent id are two separate things.
To check if a permanent is still valid, like for targeting, the controller's permanent set is checked if it stills contains that permanent, using instance or id.