Hello,
I'm not seeing what you a referring to. The -200 & -300 do not display the same max fuel capacity in the EFB.
-300: 76,511 KG
-200: 109,176 KG
Above values are valid for both engine options. As explained by @A330MRTT, the -200 has a center fuel tank where's the -300 does not, hence the increased capacity.