Travelling on H4 after H1B COs is approved

[swati]

I have had my H1B petition approved this year and it was a COS from h4 to h1b. Before October 1st I visited my home country and returned back on 1st week of september on my old valid H4 as my attorney advised me to come on my pre valid visa which was H4.

From October 1st, I have joined my company but I want to confirm that the approach I followed is logical or not. I am assuming from October 1st, my COS would automatically be done from H4 to H1B. Does a COS case need to be re applied if the person is entering on old visa?

Also, the I-94 on this time (while coming) and the I-94 with my I-797 have different numbers. Does that pose any serious concern from DHS point of view?

I have got my SSN post Oct-1st and If I am unlawful, I need the expert advice as to my next plan of action.