The subscription has now launched in Asia, but – as spotted by VGC – some PS1 games are using the PAL (Europe, Australia, New Zealand) version instead of the NTSC (Asia, America).
It appears that Sony is using the PAL version of PS1 classics in its PS Plus subscription.
By contrast, Nintendo has updated its Switch Online catalogue of N64 games to include both PAL and NTSC versions.
There’s precedence for this too, as Sony used a mixture of PAL and NTSC versions of games in its PlayStation Classic console.