The old wallet displayed the difficulty as a number which was a multiple of the minimum difficulty. That is why you cannot directly tell what difficulty relates to the old wallet difficulty for the user, as they are displayed differently, but the difficulty algorithms (Kimoto Gravity Well v2 and GroundRod Retarget PID) understand the difficulty very well, as the proof-of-work required difficulty algorithm did not change between KGW v1 and KGW v2. But after block 555555 with the change of the difficulty algorithm to GroundRod PID, the way the proof-of-work required is calculated will change and this is the reason why this is an hardfork.
In truth the PID Difficulty is a number of 256 bits such as 0x00000000010a2d19999999999999999999999999999999999999999999999999, and the PID use this number as it is, but the displayed number by getdifficulty was simplified as shown above.

nodes please?