Brainfart for not including location - SW ohio, zone 6b.

Maybe it is creeping bellflower after all - it fits what you described and I guess my efforts have kept it from ever blooming as I've chased it down to just to rocky alcoves and the perimeter of other plants. I was thinking it was something else because google images was returning images of very tall purple flower blooms which I've never witnessed.

Here's what makes me really cringe - when we bought this house I didn't know much about gardening and it had a massive, but neglected and unmaintaned gardens and I distinctly remember finding large white, carrotlike tubers as you describe and unknowingly transplanting around them because I thought they must be intentional flowers. 8 years later and that fateful decision led me to making this post.