planting 3 weeks ago is late as onions need to grow as much as possible before mid june when they start to bulb, put plant mine out in mid april. i suspect those will not bulb or be very small small if they do. as for greens they will be ok for that.

as for the remainder of the sets, you can plant them for greens but i think it is a bit hot now, i'd wait another 5-6 weeks. a few years ago a nursery had many bags of sets that they were going to throw out. this was late august or early september. so i asked for a bag and they gave me as many as i wanted, about 25 or 30 sets per bag. i took 1 bag and planted them for the greens. they grew and produced greens by mid october but of course they did not form bulbs which i knew they would not do.

for what it's worth, sets are the least desirable form of growing onions. they are onions from the prior year dug up and stored for planting this year. as such, sets tend to bolt as they are now in their 2nd year of growth and that's when onions set seeds and then die. plants are a better choice but starting from seed is the best option.

tom