diff --git a/docs/dcc-validations.md b/docs/dcc-validations.md
index 5921a01..7408514 100644
--- a/docs/dcc-validations.md
+++ b/docs/dcc-validations.md
@@ -49,6 +49,8 @@ Check back frequently as we keep growing this list of checks.  For how each rule
 
 A SAS numeric variable has 28 missing values: the regular `.` and 27 special ones (`.A`-`.Z` and `._`).  Data Controller accepts them in a numeric cell as a bare letter - `a` to `z`, or `_`, with no period - and stores the matching special missing in SAS.
 
+A numeric column that carries a date, datetime or time format is the exception.  Those cells are edited through a date picker rather than the numeric editor, and the picker accepts only a date - so a special missing cannot be typed into one of them.
+
 The rules treat a special missing as a value for some checks and as a missing value for others:
 
 |Rule|What happens to a special missing|