On the Santana bikes, if you email the serial numbers to Santana, they can tell you what year/model/size it is from their sales records. I did this numerous times before buying our first tandem about 6 years ago, a 2000 Santana Sovereign.
Also, Santana can give guidance as to risks of older-year models. I recall their steering me away from anything much older than 2000 because of some upgrade issues.
I wouldn't assume your first tandem will be your soulmate. You might get what you think is the best bike available now for your needs--to get you on the road now--before investing too heavily in it. If it isn't right, you can resell it on CR for a discount on what you paid and call it the price of learning. Or keep it as a spare, which is what we did when we bought our second, a 2005 Co-Mo Speedster Co-Pilot, when we found the Santana just a tad too small and lacking in travel couplers.
In any case: Buy a tandem and ride!