On Pottermore there’s “a list of forty names of students in Harry’s year”. There’s only one problem: Annotations aside, the list contains only 39 names.
In 2001 J.K. Rowling actually allowed us to take a quick glimpse on the original handwritten list during the documentary “Harry Potter and Me”. As you can see above, there was a 40th student who’s missing on the Pottermore list: Runcorn.
Because the other 39 students are 20 boys and 19 girls, it seems likely that Runcorn was supposed to be the 20th girl. As there are already five Ravenclaw girls on the list, Runcorn was probably supposed to be a Gryffindor, Hufflepuff or Slytherin.
Her name sounds familiar: Albert Runcorn is the wizard Harry impersonates while infiltrating the Ministry of Magic in “Deathly Hallows”. Either the Runcorn in Harry’s year is related to Albert, or J.K. Rowling just went back and used the name for a completely unrelated character. The names on the “Original Forty” list are far from final and even the Hogwarts houses of some characters have been changed in the meantime. Young Runcorn never appeared in the books or movies so she might have been cut quite early in the writing process.