That sell through rate is for the LAST 12 months, not the next 12 months. 12 months ago the domain marketplace had less than 5,000 names, it now has more than 30,000 names which is why the sell through rate is dropping almost daily. SH sell names, they are probably selling more names than ever before, but there are more names for the buyer to choose from and more names being added daily, you need to take this into account.
The sell through rate for the LAST 6 months is currently at 7.44%. If everything remains the same (amount of names added, amount of buyers etc), then you could guestimate that the sell through rate for the NEXT 6 months will be 3.6%. So, if you magically had 100 names approved today, and your personal sales rate was average, you could expect to sell 2 or 3 (3.6% next six months, 1.7% six months after) names in the next year.
Hope that helps!