Well, to be fair, since Jethro Tull is a person's name, people would be likely to assume that it was a solo artist regardless of whether this trope was present.
This would be true were it not for the fact that Jethro Tull is an historical figure known for inventing the seed drill. It's comparable to assuming that Franz Ferdinand is a solo artist.
Growing the Beard: The inclusion of guitarist Martin Barre (during Stand Up) and keyboardist John Evan (during Benefit), which greatly expanded and tightened the band's sound.
Harsher in Hindsight: Too Old To Rock 'N' Roll: Too Young To Die! marked the first appearance of Tull's third bassist John Glascock. Three and a half years after that album, he passed away at age 28.
Ho Yay: For decades a live concert staple has involved Ian Anderson sticking his flute between Martin Barre's legs in a distinctly phallic manner, and fiddling with the protruding end of it for a while. Generally this ends with a disgusted look at the free hand, then wiping it as if now covered with something very sticky.
They Changed It, Now It Sucks: More of an issue during the band's more active years. Since Tull changed its sound every few albums, criticism was pretty inevitable.