This still included other algorithmically determined tweets—from what your followers had liked and later more generally “recommended” tweets. These are no longer present in the following tab.
I’ve been on twitter since 2013 and have only ever used the OG timeline (a.k.a. chronological, a.k.a. “following”, a.k.a. every tweet from the people you follow and no others). I think there were periods where the OG timeline was (annoyingly) pretty hard to find, and there were periods where you would be (infuriatingly) auto-switched out of the OG timeline every now and then (weekly-ish?) and had to manually switch back. The OG timeline also has long had occasional advertisements of course. And you might be right that (in some periods) the OG timeline also included occasional other tweets that shouldn’t be in the OG timeline but were thrown in. IIRC, I thought of those as being in the same general category as advertisements, but just kinda advertisements for using more twitter. I think there was a “see less often” option for those, and I always selected that, and I think that helped maintain the relative purity of my OG timeline.
Technically it was a dropdown rather than a tab per se, but the option to switch to the chronological timeline has been present since 2018: https://www.theverge.com/2018/12/18/18145089/twitter-latest-tweets-toggle-ranked-feed-timeline-algorithm. (IIRC there were third-party extensions to switch back even before then, however).
This still included other algorithmically determined tweets—from what your followers had liked and later more generally “recommended” tweets. These are no longer present in the following tab.
I’ve been on twitter since 2013 and have only ever used the OG timeline (a.k.a. chronological, a.k.a. “following”, a.k.a. every tweet from the people you follow and no others). I think there were periods where the OG timeline was (annoyingly) pretty hard to find, and there were periods where you would be (infuriatingly) auto-switched out of the OG timeline every now and then (weekly-ish?) and had to manually switch back. The OG timeline also has long had occasional advertisements of course. And you might be right that (in some periods) the OG timeline also included occasional other tweets that shouldn’t be in the OG timeline but were thrown in. IIRC, I thought of those as being in the same general category as advertisements, but just kinda advertisements for using more twitter. I think there was a “see less often” option for those, and I always selected that, and I think that helped maintain the relative purity of my OG timeline.