I’ve since learned that this type of cookie is called “Evercookie”. From Wikipedia:
“Evercookie (also known as supercookie) is a JavaScript application programming interface (API)that identifies and reproduces intentionally deleted cookies on the clients' browser storage. It was created by Samy Kamkar in 2010 to demonstrate the possible infiltration from the websites that use respawning. Websites that have adopted this mechanism can identify users even if they attempt to delete the previously stored cookies.
“In 2013, Edward Snowden leaked a top-secret NSAdocument that showed Evercookie can track Tor(anonymity networks) users. Many popular companies use functionality similar to Evercookie to collect user information and track users.
“There are three commonly used data storages, including HTTP cookies, flash cookies, HTML5 Storage, and others. When the user visits a website for the first time, the web server may generate a unique identifier and store it on the user's browser or local space…Due to privacy concerns, all major browsers include mechanisms for deleting and/or refusing cookies from websites. In response to the users' increased unwillingness to accept cookies, many websites employ methods to circumvent users' deletion of cookies. Started from 2009, many research teams found popular websites used flash cookies, ETags, and various other data storage to rebuild the deleted cookies by users, including hulu.com, foxnews.com, spotify.com, etc. In 2010, Samy Kamkar, a Californian programmer, built an Evercookie project to further illustrate the tracking mechanism with respawning across various storage mechanisms on browsers.“
These are insidious and have been building up in my phone to where I now have many dozens that can’t be removed, including .ru domains even though I’ve never knowingly actually visited domains based in Russia. Despite Apple’s declaration of privacy, it’s “delete” process in the advanced settings of Safari is utterly useless against these “supercookies”.
Does no one really not care about these or know some method for permanent removal in iOS? There does seem to be methods for Mac OS.