Your table says Google doesn't specify en an encoding for the "issuer" prefix in LABEL, which is technically true. (It's a big sloppy paragraph.) However, further down the same wiki page there's an example with issuer "Big Corporation" which is shown as "Big%20Corporation".

From this I can deduce they intended issuer to also be URL-encoded, at least when necessary - and logically, the same is deducible even without that example, because an issuer could contain non-safe characters (like a space) and therefore must be URL-encoded for the sake of sanity.