If the there is adequate nitrogen already in the soil, the plants may form few nodules, regardless of inoculation. Since the plants were pulled "late in the season", it is also possible that any nodules which formed had already begun to break down, especially if the plants were past flowering stage when pulled... and pulling itself can break nodules loose. To best evaluate nodule formation, the plants should be carefully dug before they set seed, and soil gently washed away from the root ball (a hose works best for this).

When I lived in San Diego, I used a mixture of crimson clover & oats as a winter cover crop; it added a lot of organic matter when mowed & turned under.