How to find NRR status when memberships is broken

Hi all,

I'm wondering if anyone out there has an easy way to compare the NRR status year on year? Is it through t-stats? 

What complicates my task is that our memberships model has never been implemented successfully, so I'm not confident the figures I get are reliable. Is there another way to compare NRR without relying on this? I'm imagining a series of list compares, but would appreciate any guidance. 

Thanks in advance. 

Cheers,

Ben