Giant OD2 headset top bearing

So I replaced the headset bearings on my 2014 TCR Composite 1 today.
The bottom bearing was fine, but the top bearing seems to be a different height. The old bearing was 8mm tall but the new one is 6mm. Googling seems to suggest that 6mm is the correct height.
It's fitted now and seems 100%. Could it be that the one originally fitted was the wrong size? There was a lot of crud accumulated on top of the lower bearing, would this indicate that the original bearing was too tall and the headset wasn't properly sealed?
The bottom bearing was fine, but the top bearing seems to be a different height. The old bearing was 8mm tall but the new one is 6mm. Googling seems to suggest that 6mm is the correct height.
It's fitted now and seems 100%. Could it be that the one originally fitted was the wrong size? There was a lot of crud accumulated on top of the lower bearing, would this indicate that the original bearing was too tall and the headset wasn't properly sealed?
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Top Bearing should be one of these http://simplybearings.co.uk/shop/p18585 ... backstep=1
So it's got to be OverDrive2? Smaller OverDrive bearings wouldn't have fitted onto the steerer?
If it is an FSA type like this, it shows the top bearing to be 6mm deep.
http://fsa-4207.kxcdn.com/wp-content/up ... -ACB-1.pdf