I see what you mean now that you mention it, but I wouldn't have picked up on it by myself.
I get it now that you have explained it to me, but I wouldn't have thought of that by myself.
ーI see what you mean now that you mention it, but I wouldn't have picked up on it by myself.
「言われてみればそうだけど、気がつかなかった」
I see what you mean now that you mention it で「あなたがそれに言及してあなたの意味することがわかった」
I wouldn't have picked up on it by myself. で「自分自身では気がつかなかっただろう」
ーI get it now that you have explained it to me, but I wouldn't have thought of that by myself.
「言われてみればそうだけど、気がつかなかった」
I get it now that you have explained it to me で「あなたが私に説明してくれてわかった」
I wouldn't have thought of that by myself. で「自分ではそれを思いつかなかっただろう」
ご参考まで！
カナダ 
