As I said, it seems unlikely to be enabled at all, even if the logic was intended to be server-side.
If the official guidebook claims the chance for it to be granted is 1/100, we should have seen thousands upon thousands of people reporting having obtained it. To date, no one has come forward with a legitimately obtained one, including several youtubers and streamers who personally performed thousands of Surprise Trades (a statistically significant amount, the chances of them not having obtained it at least once is astronomically low if it was actually enabled) without seeing it granted even once.
We've seen very, very few people claim to have found one, and all of the Pokémon that it has been seen on so far were very obviously hacked, so the ribbon was likely assigned by cheating before it was traded, not by the server during the trade.