As far as I understand, you're asking how to know a firmware update is intended for your computer since they don't show up on the regular delta updater.
Well, usually on the download page of the firmware update, Apple posts what your new boot ROM version will be for the model you're using. Go check the bootROM version at the System Profiler. If it doesn't match for your model, you're not up to date.
Hope that was what you wanted to know.