Each AW101 variant appears to have different basic specifications which would account for the variations. This can be due to number of fuel tanks, engine selection, basic avionics fit, lightweight, durable or heavyweight floors etc. The definition of useful load is likely to include any customer specific communications/navigation systems which may previously have been included in the basic definition.
lost 836lb without modifications
The AW101 has undergone many modifications some heavier some lighter.
From my distant past I seem to remember that a basic EH101 was about 9.6t with residual oils and lubricants, the operating weight was about 10.2t.
Hope that helps.