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I would not glue them up to core wood and then glue the rest of the bow up in form later. How thin are they? If they are .030 to .050 that is normal. Just take care when applying glue and placing them with the other laminations.
If you are making a glass bow, what I do is put my glue on the glass first. Then put glue on one side of the veneer and gently flip it onto the piece of glass. Then put glue on the other side of the veneer and continue to add laminations. This is how I do it. Never have broken one yet.