Ed, I think you might be reading a little too much into the significance of the invests. The numbers we assign are more for internal tracking and data sorting purposes for disturbances than anything else. If you watch the numbers on the NRL Tropical Cyclone page, you'll see that we re-use the numbers from 90-99 over and over again.
I think the use of the invest designation started at the Joint Typhoon Warning Center when they got the Automated Tropical Cyclone Forecasting system (ATCF) back in the late 1980's. We started using them in the Atlantic and Eastern Pacific when we got the ATCF in 1989. The public didn't really see them until the invest identifiers were used to collect microwave satellite data on the NRL and FNMOC tropical cyclone pages starting in the late 1990's.
Jack Beven
Tropical Prediction Center