With TSC if you do not get a FP notice in the first 2-3 months after filing the I-485, you are in for a long wait. Most people on this board were getting their first FP notices 18 months or more after RD. It is just the TSC way of saying: "FP expire after 15 months and we are not going to touch your file for 30 months, but as we do not to do a second FP, expect your first FP to come after year and a half."
According to popular rumors TSC FP notices are generated by a computerized scheduler, which is supposed to take into account the workload of your local ASC (Application Support Center) as well as the likelyhood for your I-485 to be adjudicated any time soon.
Getting FP early use to be a blessing in early 2002 when TSC use to adjudicate cases according to the FP date, hence a lot of 2002 filers who received FP were adjudicated quickly.
It looks like TSC has finally started to work according to the RD/ND and the time of the FP is no longer important. With the vast majority of 2001 filers having had their FP in the first few months of 2003 it will be really nice if TSC could finalize these cases before the 15 months FP expiration. If they do that you should be getting your FP notice in the 1Q of 2004.