WMG / Cat's Eye

Toshio knew that Hitomi and her sisters were Cat's Eye since almost from the very beginning.

Whether consciously or subconsciously, Toshio knew the truth from the first chapters onwards. But since he loved Hitomi, he couldn't bring himself to even imagine her being Cat's Eye. Hence all his numerous mistakes while chasing Cat's Eye throughout the series was really him sabotaging his own investigation just so that he wouldn't be put into a situation where he would have to arrest her.

The girls have met Ryo Saeba at some point

Their cafe appears in City Hunter under a new ownership (as the girls have left for America by then), and Ai once noted that Toshio holding a gun with a serious face looked as cool as City Hunter. Is that enough evidence?

• If the 2019 City Hunter movie is to say anything, yes, yes it is.
• Apparently not: Ryo didn't recognize them when they showed up at the Cat's Eye. Though it's possible that the girls have seen tapes of him in action.

Hitomi hasn't lost her memory after going in the US

She's pretending to literally start a new love story (as Toshio had previously suggested when Hitomi asked him what he'd do if she was revealed as Cat's Eye) and leave the past behind, or to symbolically "steal" Toshio from her past self and give him the chance to finally "catch" Cat's Eye.