Unfortunately, I can't think of a way to hold that 500-foot Spoilerzilla in reserve, aside from omitting "Gem Type" from the character sheet--being coyly evasive on the subject would itself arouse suspicion.

One possible recourse is the Literary Agent Hypothesis: the Crystal Gems told the Crewniverse what they knew (or, in Pearl's case, were capable of communicating) at the time.