The construction was approx. 1987 so I'm assuming the applicable code is the 1985 SBC (with updates). There does not appear to be anythig in this code adressing my conditions, however, per the code, treads less than 10" require nosings. Mine are 9.5" not considering the nosings.
Maybe this photo will help explain the dimensions.http://files.engineering.com/getfile.aspx?folder=52089754-85cc-46d2-b207-3670f2ddfe26&file=IMG_6342.jpg
I have a similar case that doesn't appear to be addressed in the codes (specifically Florida Building Code). The nosing is normally 2" or so thick, allowing a vertical space of about 5" for the heel during descent as doct9960 stated.
I have not been able to find this dimension in print...