Dima,
here is quoted from USCIS website:
"Any application or petition for an individual currently in F-1 status needs to include evidence
the student has been maintaining status and has been authorized employment if applicable. Such
evidence usually can be satisfied by submitting the latest Form I-20AB/I-20ID and a copy of the
employment authorization card"
it is good to include all the copies of previous I-20s as well however, sending the latest one should be sufficient since they would not have issued the latest one have you not been in continuous legal status.
Thank you very much Khayat. You couldn't answer any better!