That's great to hear - well done that man! I'm not surprised though, in that I think, as long as that top pulley is correctly located on the cam, then the "tippex method" is entirely valid. The problem comes on older and higher mileage cars where you can be pretty sure a belt will have been done at some time and, with the likes of the Haynes manual (and others) recommending slackening that pulley, you really can't be sure that whoever did it has set this up correctly. I wouldn't automatically slacken that bolt though. Check it with the old belt still in place and see if the locking tools install. If they do then Oh Happy Day!