The page below is taken from the booklet of the Airbag/How Am I Driving? EP, and features the line "What might have been." (click image for full size):

This page appeared in radiohead.com during the Kid A period under the title 'K I N G R A T'. Apart from other lyrical fragments that would end up in the finished lyrics to 'Worry Wort', the line "what might have been" appears several times, and it's possible that the 1998 EP artwork posted above took this line from the (probably handwritten) source of this page. The original html file was created on november 1st 1999, but the text itself could be much older:

no use dwelling in whqat might have been water metalelipsicals. when im in the dark i forget the light going in a circle dead from the kneck down dead in the water frozaen in a pond take hold of my hands atissueallfalldown tell that to my face   tell that to my face crawling skeletons no use telling them   what might have been no excuses please no apologies to a walking skeleton movingin the next world say it to my face say it to my face walking skeletons and what might have been dont find yourself in doldrums dont find yourself in doldrums theres too much to be done too much to be done. no use dwelling on no use dwelling on what might have been     i am a

The line "dead from the neck down" seen in the above webpage would later be used in 'Faust Arp' and can be seen in this piece of artwork that was posted on april 19th 2007 in the Hodiau Direkton section of radiohead.com:

Another set of early lyrics, that is already more developed than the one from the 1999 webpage, appeared in the 'imaginery prisons' section of radiohead.com at the time Amnesiac was released in spring 2001:

no use dwelling on what might have beens. the candles on the cake. those powerless feelings. the flooding lakes. you're only dreaming. suicide bombers. failing missions. you stepped over the line no use looking back again. you are not thinking straight. do not let this escalate. this is not a trap. maybe you just need pinching. you are such a worrywort. what won't happen again. mistakes mistaken. swimming pool eyes. watch the human traffic. behind a chain link fence. you know how to talk how to get your way. the road you could have took mistakes mistaken. just think of all the fun you could be having.

'Worry Wort' was released on the Knives Out single and never played live or mentioned in interviews.