Are they done or can I still harvest them?

the first five pictures show plants with no fan leaves and all sugar leaves burnt up.. then the last few pics look like different plants. so are those older pics? why did you remove lal the fan leaves? this would only slow or stop development. The dead sugar leaves that i see are not cauased by your light. you overfed, more likely. since you removed the energy source of the plant, you might as well harvest them before they die on the stem. is this a 3x3, maybe light was too strong but didn't kill the sugar leaves. that would be localised to the top of the canopy and not throughout the entire plant. 600w of middle of the road efficacy lights in a 4x4 isn't too far off. If any dim needed, maybe 85-90% tops. 18-19" still might be better than 16" but probably not causing significant light burn at 16", either. QBs are better from slightly further away so that light distrubutes better from more congregated diodes. 18" is a good spot. observe and adjust power from there relative to what you see. Use resulting internode length as guide to adjust power. too stretchy - more, too tight = less.