When should the ERC-1155 Metadata URI need to be zero-padded to 64 hex characters?

Question

EIP-155 states that the "The string format of the substituted hexadecimal ID MUST be leading zero padded to 64 hex characters length if necessary."

In what situation is a 0-padded hex ID necessary? It is odd they chose to use the keyword MUST here as it seems like the choice of whether to use 64 hex character padding is completely arbitrary.

I understand that there cannot exist more than 2^256 ids (64 hex digits), but wouldn't the choice of metadata URI for an ERC-1155 token be implementation-dependent?

For example, if I wanted to create an ERC-1155 token composed only of 64 NFTs, I'd much prefer defining metadata URLs as follows:

https://{DOMAIN}/1.json
https://{DOMAIN}/2.json
...
https://{DOMAIN}/40.json (64 in hex)

Answer 1

I suspect that ERC-1155 was built with uint256 in mind as the standard for numeric types and that requiring ID to be padded to 64 hex characters means that all 256 bits of information are specified explicitly. Maybe this alleviates potential issues with dirty leading bits?

Padding doesn't appear to be strictly necessary to function - I have seen smart contracts which use unpadded metadata URLs, such as Mining.game (https://mumbai.polygonscan.com/address/0x1a3d0451f48ebef398dd4c134ae60846274b7ce0#code), (https://api.mining.game/1.json).

This is on the Polygon testnet, not a mainnet, so keep in mind that code quality may not be stellar. But regardless, it appears to work.