Hi darling,
Since nobody else has replied, I'll tell you what I remember. Unfortunately I haven't seen most of 1795 in years--the one time I watched it from start to finish was when I was living in New Haven back in 1991-92. And that is ten years ago.
I think they first use the Old House drawing room Secret Room (behind the bookcase) in this storyline in episodes that are coming up next week. In other words, during the concluding arc of 1795.
Of course the bookcase Secret Room was first used in the series in 1966 in the Matthew Morgan storyline.
It gets used in each storyline after that, I believe. In 1897, Greggie Trask and Crazy Eddy find the room using Joshua Collins' blueprints for the Old House, stored in the Collins family Library at Collinwood.
Best,
Steve