I came to US on L1 on Mar 31 2008. In April 2009 I filed for H1 and it got approved(and I continued to work on L1 status till June 30 2009).My employer filed my H1 under COS and hence I-94 came along with I797.As my project got over I went to India on June 30 2009 and got my H4 stamping done & returned to US on Sept 1 2009 on H4.I got a project now and I thought of changing my status from H4 to H1.But my employer said that as I797 has I94 attached to it and hence there is no need to apply for the COS from H4 to H1 and I can directly work on H1.If my I797 had I94 attached , i would like to know from when my H1 status became valid? If my H1 status is not valid do I need to apply for a COS from H4 to H1? Also are there any chances of me staying out of status during last 1 year.