Tonight I flew a flight where I set the clock back about 12 hours. After importing my flight plan I checked the A300's EFB (not the MSFS one), and the QNH was given as 30.00. However, when I requested a weather report at the same time from the IDC, it said the altimeter was 30.13 (the actual value in the real world at the time of the flight). So,it looks like the A300 EFB is reading the historical QNH but the IDC (and BATC for that matter) is showing the current QNH. 

Edited January 13, 20251 yr by LukeFF

To add: this also seems to extend to the takeoff performance page too.