>>12626822>because your eyes would have to be closed
Your eyes would have to be close before meeting him and never open while he's around. Remember, you see it once, and he's got you forever.
As for Ichigo's dad, iirc, didn't Shinji say the reiatsu he sensed was unfamiliar? If so, he couldn't have met Isshin in Soul Society, so they shouldn't be contemporaries.