H1 transfer on old i797 without having details of new i797 or receipt number or contacting FOIA

MY Visa will be ending in March so once my employer files for extension can I use the older i797 before the new one gets approved and comes thru? Even during this time of new petition being approved, I will not have any reciept number or any other details of the new petition. I will have the older i797 document. I am asking this because I want to know if I should apply for transfer while I still have existing valid i797 before it expires or can I do an H1 transfer to a new employer without having the i797 petition copy or reciept number or going thru FOIA. If I approach FOIA then my current employer will come to know, correct?