88 supposed to have straight G, in the desiigner signature . 89 has a flare G, in the designer signature .
its a transition year, they started the transition early, 87s have the regular G, 89s have the flare G, and in 1988, there's both reverses used, they changed it sometime that year. it's not like an error, or a mule, just a design variety for that year. 1988 With RDV-006. $5-$50 dollars I'd guess on ebay, on the higher side with correct description and nice pictures that really show it.
it's not that common to find, and a bit difficult to recognize for most people, but I'd think it happened late year, it's clearly not a 50/50 split so I dont' think it happened mid year or early year or the other would be more sought after or either/or would be equal in appearance.
After looking it up, here is a comparison image for anyone wanting a visual difference. I did not know this variety existed, so thanks @Rick Stachowski for sharing! I shall add this to my list of errors to look for! Source of image