BJU Press older vs newer Editions

Hi Everyone,
It is my first year of homeschooling my first grade, she is advanced and doing second grade mostly. I’m getting ready for the next year. She is mostly on BJU and enjoying it but its very pricey so I’m looking at older editions which sell cheaper used. Do you guys know what are the differences of older and newer editions? Specifically Reading3 and English3?

Thank you so much!