Well I'm never sure of the accuracy of Total Guitar.
This month they had a picture of the guys from Warrant with a transcription of Cherry Pie. (My Girlfriend's sister is called Cherry so this song is kind of a family in joke... anyway...) The caption said something like "24
fret guitars and spandex are out in force" above a picture of Erik Turner using a 22 fret RG Custom with the fretboard clearly in view. I think Joey Allen also tended to use 22 fretters too, he certainly is in the 92 Ibanez catalogue.
Anyway after that digressions there... The RG520 has had and if Ibanez stick to their current nomenclature will always have a twin humbucker pickup configuration, just like the RG320, RG420 RG620 and even the RG3120. The RG570 has a H-S-H pickup config, justlike the RG 470, RG670 and RG770.
the number doesn't usually dictate the body wood, that's usually independent of the number and sometimes is noted by extra letters after the guitars number.
A few years ago there was an RG570MH a mahogany RG570, where the regular one is basswood. Currently the RG520QS is a mahogany bodies/sapele topped guitar, but I believe the RG520 was available in basswood in a solid colour without a quilted top.