You're right. It was a single-only release in the UK in 1969, not on an LP until '72. However---quite a few FM rock stations in America made a practice of playing import LPs and singles back in the day (drove myself crazy trying to find Manfred Mann Chapter III's "Happy Being Me" after KGB-FM in San Diego played it one night---only to find out it was never released here in the U.S.)---so it's possible "Living in the Past" did get some FM airplay here in 1969.When I think about it -- Jethro Tull's song: "Living in the Past" wasn't on the 2nd Tull album -- Stand Up (1969).
(In fact, it may have been recorded even a bit after that album was tracked.)
I believe that that song was a hit in the U.K. in 1969, when it as first released as a single (45).
If that song wasn't on any Jethro Tull _album_, maybe no* album-orientated FM rock station in the U.S. played it (* or, at least, not much).
That changed when the double-album compilation (of the same name/title) was released in 1972.
-- Or, fill in the details (and correct me) -- if you know better or more than I do.