Even the same strain/ clone can take longer to flower/mature if all conditions arent met for that particular plant. I think you did good with the overall health of the plant. I'd personally say it was a few factors not just 1. E.g.. strain, flowering time, temps, possibly had the light too far away? Veg time or lack of plant count. Generally if you want a pound per 600w you have to really fill the canopy with colas. (And have a fairly high yielding strain) Hope ive helped. (And sorry about the pissing contest earlier with growforfun! Haha)