My spouse is doing her masters on H4 from last year. In february 2010 we applied for a change of status from H4 to F1 got the approval notice on Mar'05 2010.
"Notice Type" section is as follows

Notice Type: Approval Notice
Class : F1
valid from 07/26/2010
Valid for Duration of Status.

This is because ,the school initially issued a I-20 with a start date of 08/25/2010. Now
1. Does she falls into valid F1 status only after 07/26/2010?

2. After we got the approval notice, the International students office issued a new I-20 with start date of 03/23/2010 and is claiming that, she is into the F1 status from 03/23/2010. Is that true? Is the school elligible to do this change or do we have to send another I539 to USCIS? Is she allowed to do on-campus job rightaway?