Filing new GC case and want to use old priority date

[lucky420]

Hi - My employer might start a new GC case for me from the first stage. I already have an old case as well and old priority date.

I know I can use the old priority date. If the lawyers request retention of the priority date, and something goes wrong with the new case (denial etc..),does it mean I loose my old priority date and old existent case for ever ? Thanks!