Oops sorry: Vancouver BC. Cold last winter, very long rainy spring.

I don't think you harvested too early. If there were going to be more cloves, they would be there even if under developed. I usually have at least 4 cloves, sometimes 6. I don't think you did anything wrong since the size of the cloves looks good. Just don't replant any cloves from bulbs like this.

how did fertilize your garlic plants

About ½"-1" compost over top after planting, then mulched with leaves. Nothing more in spring.

I just read several articles after googling. Aged manure and additional fertilizer such as bone meal are suggested. I put aged manure on the bed in the spring, grow something else in the summer. When the bed is freed up in the fall I usually use a general organic fertilizer when I plant garlic. If I have a small bulb, it tends to be on the edge of the bed where I might not have fertilized well and the garlic is also competing with grass because my beds are edged with lawn.

IMHO, premature harvest, My rule is 1/3-1/2 brown leaves. I grow French Music, usually have 5-6 nice cloves, however, you had a lousy growing season. I've grown French Music for about 15 years and have read all the recomended soil amendment rules and tried to follow them. Now I broadcast 12-12-12 over the entire garden at the end of the season and in early spring. garlic is mulched heavily with grass clippings and planting site is moved every year around the garden. There used to be a "Garlic" forum here, you might want to post there and get more info from folks more knowledgable and also in your area.