could anybody help me to explain this sentence

I'm now applying for a case number for my J1 waiver. In the form DS-3035, there is one section that confuses me quite a lot. In the section of "J1 visa history", it says "if exchange visitor's status changed to J1 while still in the US, enter date of status change, control number and issuing post of that first J1 visa". Here comes the confusion. If the status is changed within the US, is it possible to have a control number for the new status?? Since there won't be any visa needed if you change your status within the US, why it still requires a control number which you can only find in your visa stamp??? Or I have been misunderstanding it??

Please help me to explain this. Your reply is greatly appreciated. Thanks.

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• 回複：could anybody help me to explain this sentence?? -知音96691- ♂ (77 bytes) () 06/13/2007 postreply 16:14:26

• 回複：回複：could anybody help me to explain this sentence?? -geyy- ♂ (62 bytes) () 06/13/2007 postreply 16:43:14