Myself, I do quite the opposite. I glue on tip overlays prior to tillering, but usually just after floor tillering. I find it a waste of time to shape the tip of the bow twice: the first time to make a temporary string groove, and the second time to make a definitive groove in the overlay as well. To add to that, it's likely that you rounded the corners for the temporary grooves. That means that gluing on the overlay is not going to be so neat, because the rounded corners and grooves create less surface area for the overlay. I just find it easier to glue on overlays on a flat, untouched surface of a bow tip which has not yet been shaped.