My fiancee had C1/D visa and she has been to USA several times as a cabin crew.
We are currently filling out DS160 form and they ask for all the dates and length she stayed in USA.

1) We noticed that are no US entry stamps on her passport whenever she entered USA
2) We also trying pulling out i94 records but no records are found. I am assuming that C1/D visa holders are exempt from i94?

Basically how can we find out all travel history to USA?
Thanks a lot