4DS - Anything but Charting, page-27780

With DM confirming tuneability is via process changes, can only mean they've made multiple variations of the cells and are currently testing all variations within the array to find the variation with the best metrics to suit requirements for storage class memory. This will be why testing is dragging on. Once they've narrowed the field they can focus on on deep accelerated testing on best variation, and get imec to confirm metrics for same.
Just hold people, we're in good hands with imec, best on the planet. Trust the process.