Here's the weird thing as far as I'm concerned, we have all these Champ made filters with many similarities like Amsoil, Royal Purple, and TRD PRO as well as Mobil 1, Champ XL, etc but despite their similarities there are differences in what is reported with things like filtration efficiency.
For example I cannot say conclusively that the royal purple and amsoil filters use the exact same filter media, however Ascent Filtration's testing has shown that the Royal Purple performed marginally below the Fram Ultra (which is 99% @ 20 microns) while another filter rated at 99% @ 25 microns (Purolator Boss) had noticably lower filtration efficiency as compared to the Royal Purple per testing results.
My point being that I surmise that the current version of the Royal Purple oil filter is likely closer to the, if not the exact same, filtration efficiency reported by the Amsoil oil filter being 99% @ 20 microns or thereabouts. Now Royal Purple on their website claim filtration efficiency of 99% @ 25 microns but at the same time this product has undergone some substantial revamping in recent times so perhaps whoever is running their website might just be behind the times when it comes to updating their information.