According to WikiPedia and confirmed by the National Weather service, INVEST tags on weather systems mean the following:
Invests are designated by three separate forecast centers: the National Hurricane Center, Central Pacific Hurricane Center and Joint Typhoon Warning Center. The designation of a system as an invest does not necessarily correspond to any particular likelihood of development of the system into a tropical cyclone. Invests are numbered from 90 to 99, followed by L in the Atlantic, E and C in the East and Central Pacific respectively, or W in the West Pacific.
The numbers 90-99 would be used to identify specific systems. Once the last number, 99, is used, the next system would receive the ’90’ designation alongside it’s geographic label (L, E, C or W.)