DMPはどのようにCookieデータを収集しているか（オフラインデータ編）より
「オフ」ラインから「オン」ラインへのデータsyncは30-40%くらいという説明。
妥当感はある。
さらなる元ネタはこちら↓
Unfortunately, the overlap between sources tends to be small, typically 30 – 40% of the total offline records on a good day. It depends how often users delete their cookies, and how often they visit the site.
引用元: Data Management Part IV: Syncing Offline Data To Your DMP – Ad Ops Insider.
