Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_51250 ( "Year" real, "Date" text, "Winner" text, "Result" text, "Loser" text, "Attendance" real, "Location" text )

### Question ###
what date saw the chicago bears lose in green bay earlier than 1931?

### Accurate SQL ###

SELECT "Date" FROM table_51250 WHERE "Loser" = 'chicago bears' AND "Location" = 'green bay' AND "Year" < '1931'