The Ada programming language is defined by ANSI/MIL-STD-1815A, approved 22 January 1983. (It subsequently was approved as an ISO standard.) Every ANSI standard must be reviewed after five years. Then a decision must be made either to abandon the standard, renew it without any changes for another five years, or begin a revision process. The Ada Board decided that “some omissions, limitations, and minor errors have been discovered … since the ANSI standard was approved. Although a major revision does not appear to be necessary to correct these problems, some revision is warranted.”
The Ada Joint Program Office (AJPO) established the Ada 9X Project Office in October, 1988, to revise the Ada language standard. The designator “9X” comes from the habit of referring to the Ada standard approved in 1983 as “Ada 83,” and the expectation that the revision will be approved in “199X,” where X is unknown.

ESC_1992_Vol2_Page59_Jones_Ada 9x.pdf