Hopefully it is my mistake, but I did know about the random placement, and I have attempted three times in a row to pass this part of the level. I am unable to open either of the two remaining chests/drawers/boxes with the two keys I have, and I am pretty sure that I have found and opened everything that I did during the session when I was able to locate that 'missing' note! I will try again tonight and update here if I am able to get past this.
My apologies if I have made an error. I don't want to put anyone off buying this. It is an absolute steal at $2.99!