Prolonged ferment - fantastic yield

[cwrw]

I turned out an AG Duvel type beer and it fermented for three weeks (!) using a brewferm Abbey yeast clone and the reading I've taken brings it to 10.1% alc (before I place it in the bottling bucket)!
When I've hit all my target gravities prior to fermentation,and used a yeast that I thought might just manage 8%,apart from innacurate measuring equipment what could have caused this pleasant addition of 2% on top of my quota? :wha:

 

[cwrw]

The laugh's on me, as I discovered whilst I was bottling that I'd lost three litres from moving to secondary and then to Bottling bucket. I assume my loss has also come from prolonged fermentation time within a warm environment due to evaporation . Oh well..you live and learn!