"It's declassified but I'm going to keep it secret." I'm not going to show you and will hold it till it may come in handy in defending me from false accusations.
And Trump can try to make that argument, but he will have to convince a jury. Maybe listening to the tape would make a difference because there can be different inflections and nuances in the spoken word versus the written word. Based on reading the transcript, I would not buy that as a defense without something else to back it up.