ATF Replacement - Oil Volume

[Heineken]

Well, I feel a little unsure about asking this question here but I would like to clarify something I observed.
AT NSX are quite rare in Europe but I'm going to try my luck :-)

Currently I'm in the middle of refurbishing my driveshafts (detected the typical grease decomposition signs when changing oil this spring). It was advised to drain the ATF before removing the left drive shaft, which I did. The amount of drained oil was ~3 liters. This matches the data given in the repair manual.

As I was missing a replacement washer for the drain bolt, I bought one about two weeks later (currently a little busy). To my surprise, another 1.5 liter of oil came out of the transmission when the plug was removed. Beside the fact, that I'm now in need of buying even more ATF I would like to ask the more experienced readers whether this is normal or where the extra oil came from.

I'm aware that the transmission holds ~7 liters of oil but I assumed that it was stashed away in cavities and other dead ends inside the housing and not simply draining out given enough time ..