Do geshe degrees change over time?
The difference between the geshe degrees is comparable to the grade you get on an exam. 

From TibetCulture.net:


  Geshe Lharampa is the highest degree of the Geshe system, equivalent to the doctorate degree in Buddhist studies. The other three lower-level degrees, namely Dorampa, Lingtse and Tsorampa, will also be conferred according to candidates' performance in the dialectical debate.


And:


  Such a challenge as it is, it usually takes decades for a few distinguished lamas to succeed.