Working out which model of Spector bass guitar you have can be very difficult if there are no clear indications on the bass itself. Learning the differences in the printing of the serial number can point you to an era in Spector's production, which then can guide your search for your model. Stuart Spector released his first bass in 1977, the Spector NS-Bass, and many models have been made since then. Identifying your Spector bass model by the serial number is easy to do, but it more often revolves around the printing style than the number itself.
Check the bridge on old-looking basses. The serial number on the original Spector basses was either engraved into the bridge, or written inside the control cavity. The earliest models had serial numbers that were based on the date. As a result, the year is easy to identify. These are part of what is termed the "Brooklyn Era," which spanned from 1975 to 1985. The later models in this era, however, had sequential (not date-based) serial numbers printed in the wood on the back of the headstock.
Look on the back of the headstock for a serial number on all other basses. As a result of Spector espousing a sequential serial-number system, the only way to tell different eras apart is by what is printed beside the serial number. Look for a serial number stamped with ink beside a "Made in USA" label to identify a bass as being from the "Kramer Era," which was 1985 to 1990. The serial number on these models is often difficult to make out, because of the ineffective stamping method used.
Check the headstock for Stuart Spector's signature. This is only present on models made after 1991. These models are part of either the "SSD Era" or the current era of production. The "SSD Era" was 1991 to 1998. All of the models with Stuart Spector's signature on the headstock also say "Woodstock, NY" on them. Aside from these details, these models also include a serial number --- still sequential in construction --- and a date. Next to the date, there is also a model number. This is the model of your bass. The model number will be something like NS-1 or SD-4.
Browse through Spector's "Models Through the Years" pages to find your bass (See Resources). The models are arranged according to era, which you should be able to discern based on the printing on your serial number. Click the desired era and scroll through the information on the basses until you find your model. There are pictures for each model, which should help you identify your bass quickly.
Contact Spector if your model has no serial number or has a printing method not listed here. E-mail them at firstname.lastname@example.org with information about your bass, and they will attempt to identify it for you.
International models generally have the serial number printed on the back of the headstock, apart from the models made in Korea in 1975 to 1985 (the Korean "Kramer Era") and gloss white models. Gloss white basses will have the serial number printed on the control cavity cover.