I'm not sure if the original poster is asking if a pilot can hold type ratings in multiple types of aircraft, or if the poster is asking whether one type rating can be used for multiple types.
Yes, a pilot can hold multiple type ratings.
Yes, some type ratings are good for several different aircraft.
I hold type ratings for various airplanes. These type ratings are specific to those airplanes. My B747 type, for example, allows me to fly a "Classic" Boeing 747...I can fly a B747-100, B747-200, or a B747-300. I can't fly a B747-400, however, because that's a separate type rating.
I'm typed in a Learjet. My type rating allows me to fly a Lear 23, 24, 25, 28, 29, 31, 35, 36, and 55. Other Learjets such as the 45 and 60 require a separate type rating.
The Lear type is somewhat unique, because unlike other type ratings, there are very significant differences between 20-series and 30-series learjets. They really should have been separate type ratings. Most type ratings (such as the 747, above) involve airplanes that are so similiar that one type rating easily covers them. The Learjet, however, has very different handling characteristics...especially the early unmodified Lears of the Learjets with early wings. The 20-series are real rocketships compared to the 30-series...and even in the 30-series there's a difference in handling and performance between a Lear 31 and a Lear 35. It's all much more than simple switch locations of systems. The aircraft systems are all very similiar, but the way in which they're flown and what they can do are different enough that they should have been separate type ratings (in my opinion).
Some types will allow several aircraft on one type rating. B757 and B767, for example. Others will not. I originally went to school on a Sabreliner 60...but was later introduced to the Sabreliner 80...different engines, different airplane. Even though there are many commonalities and similiarities...different airplane. Some type ratings apply to other aircraft in the same family, some do not.