V1[]
Indications are, DTREAD in SmileBasic V1 is identical to that in V2.
V2[]
DTREAD(string),variableY,variableM,variableD is a command which takes a string representing a date (as the DATE$ system variable), and sets the variables to the year, month, and day-of-month represented by the string.
In particular, the string must be 10 characters long, the fifth and eighth characters must be "/", and the remaining characters must be digits. The year can have any value from 0000 to 9999, and the month and date can have any value from 00 to 99, so it will parse strings which do not actually represent a valid date.
See also TMREAD (Command).
V3[]
No information on SmileBasic V3.