Find face after extrude

I have a problem with keeping face indices between face-changeing operations, need help/suggestion (
I`m getting list of faces in bmesh, remembering thier indices and then extrude them one by one. The problem is that after updating bmesh lookup tables old indices to non-touched faces start to point on newly added faces!

How i can find new indices of faces, that are NOT affected by bmesh updates (after face-extrude operation for example). Any help really appreciated

Just found by myself - unaffected faces objects are not deleted during bmesh transforms (even when indexes does). So keeping references to them allow script to do what is needed. even after reindexing