Re: Japanese 2002 RG1570 vs Korean 1998 RG420FA
Second, your 1570 would be considered a 2003 despite the 2002 serial. This is actually totally normal as Ibanez launches new models on January 1st and they need guitars ready, so their production year doesn't really align with the calendar. Sort of like how the US government Fiscal Year 2019 started on October 1, 2018. Your serial number probably has the last 5 digits 33xxx or 36xxx.
Regarding the frets, I've found a reasonable amount of variance in the width of frets but the height is usually pretty consistent. A new fret should be 0.058" tall and I've seen them that way and I've seen some that are more like 0.055", but I'm 99% sure these have been leveled.
A 2018 RG550 has frets which are 0.118" wide, which would correspond to Jescar FW58118 wire. However an RG1570Z neck with a 2013 serial has frets measuring 0.113" wide, which is the same as a 1990 RG neck. I would assume your guitar has frets similar to one of these. Not certain where those might come from?
I've never seen an RG where anyone would consider the frets narrow. If your guitar looks like it's been played a lot, it's entirely possible it was refretted with smaller wire.