Thanks!
Thanks for the answer from stp and Bodd !
I found pub 519 page 7 said: "If you qualify to exclude days of presence as a student, you must file a fully completed form 8843 with the IRS."
My LG didn't file 8843 for 1999, but he counted 1 day for 1999 in the 8843 forms from 2000. So this is OK, right?