Questions 29 and 30 in D-156

[cka]

Hi,
I am trying to apply for a visitor's visa for my parents.
When filling my mother's D-156 form we are unsure about the details to answers to questions 29. (have you ever been to the US) and 30. (Have You Ever Been Issued a U.S. Visa? ). The answers to both the questions are a 'yes' but we do not remember when exactly she was in the US the last time. We just know it was somewhere in the 1960's. Also we do not remember the date on which her visa to the US was stamped. The details to both those questions were in her 1st passport which we no longer have.
How do we get around this problem? Kindly advise.
Thanks,
C'ka.

[txh1b]

Write the same in the DS156. She can explain to the VO.

[cka]

Write the same in the DS156. She can explain to the VO.

The form requires that you enter date on which the visa was issued and how long you stayed in the US. Can I put in any date just to fill the columns and then include the cover letter?
Thanks,
C'ka.

[txh1b]

The approximate date is always better. She should remember the month at the least. Does she not have a copy of the old passport?