September 1993 is known on Usenet as the September that never ended. Thus, for example, the day this question is being posted is Saturday, September 8740, 1993.
Your program or function should take any Gregorian date (with positive year) as input and return the same date as output if it's prior to September 1993 or the date on the September 1993 calendar if thereafter.
You may accept YYYY-MM-DD, YYYY/MM/DD, MM/DD/YYYY, DD/MM/YYYY, D-Monthnameabbr-YYYY, or any other popular format that uses the entirety of the year (as opposed to the year modulo 100). You need only accept one such format, of your choosing. Output format must match the input format.
Sample input → output:
- Sunday, 6 August 2017 → Sunday, 8741 September 1993
- Tuesday, 28 January 1986 → Tuesday, 28 January 1986
Or:
- 2017年08月06日 → 1993-09-8741
- 1986年01月28日 → 1986年01月28日
In the interest of more interesting answers, the use of a built-in function designed for this purpose (such as the UN*X sdate command) is disallowed. Aside from that and the standard exceptions, this is golf, so the shortest answer wins.