Those two mnemonics opcodes are known to have the same timing / same inner mechanisms of mapping into HL.

It is obviously a bug in documentation from the [link] you give us. Those two pages you mention (86 and 87) were certainly edited based in the HL instruction, and someone forgot to edit that value to reflect the IY timing.

Also, do not focus much in single details. If they have the same T times described, they shant have different execution times in the theoretical times in the datasheet.

[link]: http://www.zilog.com/force_download.php?filepath=YUhSMGNEb3ZMM2QzZHk1NmFXeHZaeTVqYjIwdlpHOWpjeTk2T0RBdlZVMHdNRGd3TG5Ca1pnPT0=