Last year or so, I read a brief article about this, but I have forgotten where that was. It might have been in an APA that I take which only about 14 members belong to so very few people would have seen it. Anyway, I believe the person was explaining that the series lasted from "The Way Back" to "Blake" as anywhere from seven years to ten years. And they did a detailed job explaining how that was so.
I do seem to recall (with my terrible memory) that one comment regarding Dr. Plaxton was important in the calculations. IIRC, Dr. Paxton has been with the Space Rats for three years, ever since the Andromedan invasion.
I think it is an error to assume only four years passes because only four years passed in the actual making of the series. The Blake of "Blake" is definitely more than two years older than the Blake of "Star One," IMO.
However, in my writing, I am very inconsistent and I am definitely guilty of assuming that only four years passes since that is the easiest and laziest way out. However, in general I try to keep the time vague and whenever possible don't get into exact ages of the characters in my PGP stories.
Joyce