mGBA libretro core accuracy on other emulators than Bizhawk

[Gnuk]

Hello,

I discover some games in speedrun.com have those rules : 

Code:

-Bizhawk with mGBA core is the preferred emulator, regular mGBA is also allowed but less recommended.

-Any other emulator will not be accepted for the leaderboards

So I tell the players on discord to understand why libretro mGBA core is not allowed for other emulators (like retroarch for example) and they answer me :

Code:

It's due to inaccuracy. Bizhawk with the mGBA core was found to be most accurate. We had other emus saving 30+ seconds due to running improperly which is a huge margin in a 15 min run

So i don't understand why any other emulators using mGBA libretro core could have a different accuracy :

Can you help me to understand if another emulator like retroarch using mGBA libretro is really less accurate and why ?

[endrift]

I have no idea. Might be human error or different versions of the core.