User blog comment:God of nothing/Shiba clan logic/@comment-8891571-20130429044719/@comment-2182964-20130513200653

Having "punk-ass reiatsu" wouldn't necessarily be enough for anyone to make the connection between Ichigo and Isshin. We all remember when Byakuya fought Renji? Rukia only recognized the spiritual power as Renji's when his spiritual power returned to a lower level, as it was what she was familiar with. The same could probably be said of Isshin when he appeared and handed Aizen his ass on a silver plate; though in this case the reverse is true. Isshin's power was reduced since his time as a Captain, meaning the Gotei 13 simply failed to go: "What!? That's Isshin Shiba!". My view anyway :)