There is no rule against holding several certifications at once, as long as your facts genuinely support each one you claim (see which certification is worth your time if you have not sorted that out yet). A woman veteran with a service-connected disability whose office happens to sit in a HUBZone can hold WOSB, SDVOSB, and HUBZone at the same time, because each program tests a completely different set of facts: ownership and gender for one, veteran status and disability for another, location and residency for the third. Qualifying for one does not use up your eligibility for another.
What stacking actually buys you
Each certification opens its own separate set-aside pool. A HUBZone set-aside and a WOSB set-aside are two different competitions with two different eligible fields; holding both certifications does not combine them into a bigger chance at either one, it means you can enter both. Think of each certification as a key to a different room, not a bigger key to the same room. More keys only help if there is something worth walking into behind each door.
The question that actually decides it
A certification pays off only when agencies actually run set-asides of that type for work in your trade. This is where stacking goes wrong for a lot of businesses: they add a certification because they qualify, not because the demand is there. Before pursuing a second program, look at how many set-asides of that type have actually posted in your NAICS codes. If your trade sees three HUBZone set-asides a year, HUBZone is a hobby, not a strategy, no matter how easily you qualify for it. The certification worth chasing is the one where the pool it opens has real water in it.
What stacking costs, beyond the application
Every certification comes with its own upkeep: HUBZone recertifies every three years and can be checked in between, 8(a) runs a nine-year clock that starts once and does not pause, WOSB and SDVOSB carry their own renewal and documentation cycles. None of that is expensive in dollars, most of it is free to apply for and free to maintain, but it is attention, spread across however many programs you hold. Stacking three certifications means tracking three sets of facts that can drift out from under you, not one. Add a program because the volume justifies the attention it will need for years, not because the application looked easy.
Check volume before you apply, not after
Look at what has actually posted in your industry codes before spending time on a second application. Once a certification is on your profile, Quarry matches every set-aside of that type against your NAICS codes automatically, which is a reasonable way to see, in practice, whether the pool a certification opens is actually worth what it costs to keep.