Unoriginal research in Statement of Purpose
I think most admissions committees will be aware that undergraduate work is not likely to be groundbreaking. 

Instead, emphasise the "soft" skills you learnt while doing the project; for example, independent learning, communication and team work, and how to build a good working relationship with a supervisor. 

It would also be a great opportunity to discuss how your project led you to be interested in pursuing research at PhD level- did you enjoy discovering new things for yourself (even if they were 20 years old)? Did your work in that area spark off a particular new interest in statistics? Does the work have any modern applications? 

Discussing things like this will show the person reading your statement that you have put thought into your decision to apply for PhDs, and how the work done in the past links to the state of the art (knowing how to avoid reinventing the wheel is an important skill for a researcher).