It is cryptographically signed, so creating your own QR code that would be accepted by the apps would be difficult without the signing key.
Even ignoring that though: including both the ID and detail allows it to work both ways. In official situations (e.g. at a country border) you might be able to validate against a server, but the local nightclub probably doesn't have access to a validation server.
Even ignoring that though: including both the ID and detail allows it to work both ways. In official situations (e.g. at a country border) you might be able to validate against a server, but the local nightclub probably doesn't have access to a validation server.