Estimating over my entire ~40yr career, I'd say about 1/3 of that time was on projects that were never released. However, much of that work was reused/repurpose

Estimating over my entire ~40yr career, I'd say about 1/3 of that time was on projects that were never released. However, much of that work was reused/repurposed for other projects later. I'd estimate that about 1/5 of my code went entirely unused in the big picture.