I'm a new user who added only 1 part.
When I use "BUILD SEARCH", it shows that I can partially build 500 sets with up to 22% completion. This is obviously wrong.
The root problem seems to be with handling minifigs and stickers - the numbers are as if I had all the required minifigs/stickers, which inflates the numbers. If the set has 1000 parts and 100 are minifig-related, then the set would be shown as 10% complete, since 100=10% of the parts are "not missing".
A better way to handle this would be to ignore minifigs in both the number of required parts and the number of available parts. This way I'd get 0% for all sets.
An example with current behavior (remember, I do not have any parts):
Missing: 893 of 1145 parts
Story Starter Core Set
Educational and Dacta2013