That's what a afc is for: lies to the ecu. The SR ecu is old so it does not change over time like the WRX ones'. If your engine is running fine, let it be unless you are upgrading or trying to turn up the boost.

Z32 MAF without tuning: VG MAF and SR MAF reads airflow differently (The unit is different). So even with the same number, the feedback from both MAF is different. And this makes your engine running rich/lean.