Cao, Thor, thanks for confirming that something is amiss in my endeavour.
Indeed I do use the excel spreadshets from Harris Cyclery. The results from this tool are reasonable.
I've rechecked the lacing and looks good. I rechecked all dimensions on the hub and the ERD as well.
I am beggining to question the 6 spoke length verification method. Is lacing 6 spokes to verify their length something one can depend on? Maybe this method is faulty? It's described in The Bicycle Repair Book by Rob van der Plas, this is what yielded me the 19mm difference in results.