I've been playing Midnight Mansion for years and I'm only able to get a 93% completion rating in Spider Palace Easy. I don't want to know where the missing secret is, but I have a few questions about what I have found, in the lower right corner pathway there are no secrets found, though in room 16901 there is an area which in other parts would be considered as a secret location but is not record as such here. Is there a secret location in the lower righthand corner area?

It is possible to get all the secrets (see the high scores list at www.actionsoft.com/mm/hdscores/scores.php?m=11).

If by the lower righthand corner area you mean the part entered through room 17100 the answer is that your missing secret(s) may be found there.

The room I start in is room 16499 and in the lower right-hand corner is the doorway to room 16500 where I found what should be a secret area but is not recorded as such, I've not found and secrets in this area.

I agree there are no secrets in this area. Presumably what you refer to as a secret area is room 17101 which you enter from the room above, 16901. The access in room 16901 is marked by some bricks with a slightly different pattern to those around them and I think the designer of the mansion thought this was a good enough clue to indicate there was something significant about those bricks and he expected people to investigate them.

As far as I remember most of the 'real' secrets in this mansion are found by walking through what appear to be solid walls which don't have any indication that there is something on the other side of them.