What you're probably noticing
A tenant complained about a musty smell in a unit, or a maintenance crew pulled out a section of drywall near a bathroom and found it soft and discolored. Someone patched it, painted over it, and called it done. Before you sign off on that repair, it's worth slowing down, because in Los Angeles the conditions that caused the damp in the first place rarely go away just because the wall looks fresh again.
Southern California doesn't get much rain, but the rain it does get tends to arrive in short, hard bursts between November and March, and a lot of local building stock, especially the stucco-over-wood-frame apartment buildings and dingbats built from the 1950s through the 1970s, was never detailed with much margin for water intrusion. Add decades of deferred maintenance, flat or low-slope roofs that pond water, and HVAC systems that run constantly in the dry months and create condensation in the wet ones, and you get a housing stock that hides moisture well and dries out slowly.
Why a patched wall isn't proof of anything
Painting over a stain or replacing a piece of drywall addresses what you can see, not what caused it. Mold doesn't need a flood. It needs sustained moisture, somewhere in the high 50s to 60s percent relative humidity or higher, and a few days of still air. Coastal fog in the morning, marine layer that doesn't burn off until noon, and buildings that get shut up tight for air conditioning in August all create exactly that kind of microclimate inside a wall cavity.
If a contractor's invoice says they removed moldy material and repainted, ask what moisture reading they took before they closed the wall back up. A reading on drywall or framing lumber should be close to what's normal for dry lumber in this climate, generally well under 20 percent, before anyone reinstalls insulation or drywall over it. If there's no reading on record, there's no way to know whether the repair sealed in a problem instead of solving it.
More on this from Reading List What A Property Manager Should Ask For Before Signing Off A Damp Repair.
What a property manager should actually ask for
Before approving payment, ask for the source of the moisture, not just the symptom. A stain under a window after a January storm might mean failed flashing, a cracked stucco control joint, or a roof drain that's been clogged with eucalyptus leaves and jacaranda blossoms since spring. Each of those is a different repair, and painting over the stain fixes none of them.
Ask for photos of the cavity before it was closed up, and ask whether the repair included addressing the entry point, not just the damaged material. In a building with a history of roof leaks or plumbing issues, this matters even more, because mold in one unit is often a preview of what's happening behind the wall in the unit next door or the one below.
Ask for a clearance test after remediation, done by someone other than the company that did the repair work. This is standard practice in commercial and multi-unit settings precisely because it separates the person doing the work from the person confirming it worked. A clearance test checks air quality and surface samples against a baseline, usually outdoor air sampled the same day, to confirm spore counts inside are back in line with what's normal outside.
What you can check yourself, and where that stops
You can walk the building after a rain and look for water staining on ceilings near roof penetrations, around skylights, and along the tops of exterior walls where stucco meets the roofline. You can check under sinks and around water heaters for slow leaks that nobody has reported because they're small enough to go unnoticed for months. You can ask tenants directly whether anyone notices a musty smell, particularly in north-facing units or ground-floor units with crawl spaces, since those get less sun and dry out slower.
What you can't do yourself is sample the air or the wall cavity and interpret the results. Mold species matter less to most repair decisions than moisture conditions and extent, but when there's a dispute with a tenant, an insurance claim, or a question about whether a repair actually worked, you need documented testing from someone with no financial stake in the outcome of the repair itself. That's the point where this stops being something a maintenance supervisor can sign off on with a flashlight and a nose, and becomes a job for an inspection that produces a written report you can hand to an insurer, an attorney, or a worried tenant.
Why this matters more in a rental building than a single house
A homeowner can live with some uncertainty about a repair in their own house. A property manager overseeing multiple units can't, because mold complaints in rental housing in California carry habitability obligations, and because one undocumented repair makes every future complaint in that building harder to resolve cleanly. A clearance report and photo documentation from the original repair aren't paperwork for paperwork's sake. They're what lets you say, with evidence, that the problem was actually fixed, not just hidden until the next wet winter brings it back.