The more important thing is the crank arm clearance at the chainstays. It ought to be moreorless symmetrical.

AFAIK: JIS/ISO taper is the same taper. Only ISO tapers smaller and thus the spindle measures a bit longer for a given crank inboard/outboard position.

Sometimes the spindle is asymmetrical. This mostly comes up in older loose spindle applications. A common bike shop hack is to flip the spindle 180 degrees (reverse left/right) when converting to/from double/triple installations for chainring to chainstay clearance.

You need not make too much of it unless the pedals are egregiously out of symmetry. +/- a mm or 2 could simply be crank arm tightness & manufacturing tolerances of all the various pieces involved.

I agree that the drive-side flange is on the drive-side. Very unlikely for a sealed cartridge unit to be installed backwards.