The definition of the vaule of "2 sheep" and above often varies.
In fact, there is a LOWER rating than "no sheep".
The very worst drives for protected backup, cannot even write RAW.
So at no sheep, you can replicate errors (original Safedisc).
At 1 sheep (the start of the "weak sector" battle) you can replicate the less severe "weak sectors" of early SD2 versions
At 2 sheep, you could replicate the known weak sector patterns of the time (SD 2.51)
In the common parlance, a "2.5 sheep" writer is able to handle the additional weak patterns used in SD2.9
And the legendary 3 sheep, would be able to handle all possible weak sector patterns.
Since Elaborate Bytes and their maintainence of the "sheep table" were driven out of the field by European legislation, the definitions above that level are rather fuzzy.