I read several times about the hypothesis, also reported on Wikipedia, that ageing is linked to the length of the telomeres. Each time the chromosomes are duplicated during a cell split the telomeres lose a little bit of their length and their ability to drive further duplications declines.

But now I read the story of Henrietta Lacks' cells. Her cancerous cells where harvested 70 years ago and they have been used to create thousands of cell lines. Since she was 30 years old when the cancer was discovered those cells now might be 100 years old. The real age is probably less because most of them were frozen from time to time, but on the other hand they are cancerous cells duplicating at a frantic pace.

I read from this answer that cancer cells can activate telomerase and restore the telomeres, but is it still happening after so many years? In all the cultivations in vitro did were they always provided with the right nutrients to produce telomerase?

Is there a study on the status of the telomeres in those cells? Are they really "eternal" in practice or the definition of eternal is still in theory?