Why set-aside filters mislead you
A set-aside filter shows you the finish line. It hides the notices that have not decided where they will end up yet.
Filtering SAM.gov down to only the set-asides you qualify for feels like the obvious move. Why look at competitions you cannot win? Two honest problems with that logic cost people real opportunities.
You are allowed to bid full and open too
Qualifying for a set-aside does not restrict you to set-asides. A full and open competition, or one set aside for a different category entirely, is still open to you, you are simply competing against a wider field for it. Filtering those out of your search means never seeing work you were always allowed to chase, some of which draws a thinner field of competitors than you would expect.
A sources sought often has no set-aside yet, and that is the point
Many sources sought notices post before the agency has decided whether the eventual solicitation will be set aside at all. That decision often depends on the responses the sources sought collects. Filtering sources sought notices down to "my set-asides only" hides exactly the notices where responding could get the future competition set aside for you. See responding to a sources sought for what that response should say.
Blank does not mean large business only
The set-aside field on a notice can be blank, unset, or labeled inconsistently, and that is usually a data problem, not a decision about you. The field gets filled in by whoever wrote the notice, and it is not always filled in carefully or the same way twice. Reading a blank set-aside field as "not for me" throws away notices that may be entirely open to you, or that simply have not had the field filled in yet.
What to filter on instead
NAICS code is the reliable filter, because it describes the work, not a status that can be blank, wrong, or not yet decided. Use set-aside as something you read on each notice once you have a shortlist, not as a gate you apply before you have looked at anything. See searching SAM.gov without drowning for building that kind of search.
The honest version
Quarry reads every open notice in your NAICS codes and treats the set-aside field as one input into the verdict and the reason behind it, not as a pre-filter that decides what you ever see. A notice that is not set aside for you yet might still be worth a look, or worth a response now that could change what it becomes.
The short version
A tight set-aside filter feels efficient and still leaves real opportunities unseen, because the field is inconsistent and some notices have not been assigned a set-aside yet when they first post. Quarry reads every open notice in your NAICS codes and weighs the set-aside field into the verdict rather than using it to decide what you see at all. Deciding whether to respond, to a sources sought especially, stays yours.