OH boy! I've done that ... on my most recent quilt I added too many blocks to two of the rows ... then when I got to the last row, couldn't figure out why I ran out of blocks ... shrugged my shoulders and made more blocks ... (I was paper piecing) ... when I went to sew all of the rows together I figured out what I did when two of them were WAY too long!!!!!
And I did that just yesterday LOL