I know for sure they were produced in 1988, but I have a feeling that they may have been produced in '87, 'cause I'm pretty sure that the e39a bodyshell was first produced in '87, so it's possible that's when the first VR4 was made. But they were definitely around in '88.
1987 was when the first JDM VR4's were built. I own an 88, but have seen a few 87's around. they are the same as the 88's. Have different spot/corner lights, tail lights, spoiler and interior to a 90+ JDM. But the paint doesnt seem to crap out on the silver 88's like it does on the silver 90+ ones :P