A county spokesman, David Wert, conceded that treatment approval had been balky and slow, but he said the county did not want to deny anyone needed care.

“We’re very frustrated at the system, and by the fact that our employees are not happy with what’s going on,” Mr. Wert said. County workers check in regularly with survivors, trying to resolve their problems, he said, and “we’re actually in the process of hiring a dedicated workers’ comp liaison to work solely with these people.”

Both sides say that part of the problem lies with the state workers’ compensation law and the guidelines for applying it, which anticipate common workplace injuries like those resulting from a slip and fall, not those seen in a war zone. The guidelines say treatment cannot be denied just because a condition is not explicitly mentioned, but in such cases, decisions become less straightforward.

California and several other states have also changed their workers’ compensation laws in recent years, in ways that curb benefits and save employers money. A 2013 change in California removed the option of appealing a denial of coverage to a state administrative law judge. This makes the process faster but also means that denials are reversed much less often.

“The guidelines in the law are one-size-fits-all, which doesn’t work for unusual cases, and we used to have the ability to convince a judge of that,” said Marc G. Marcus, a workers’ compensation lawyer in Sacramento who is not connected to the case. “What’s happening to these people in San Bernardino is just a very extreme example.”

Ms. Baker, the state industrial relations director, said the system had become more stringent because “there were huge abuses,” with doctors prescribing unnecessary treatments. And some San Bernardino survivors’ claims were denied because providers had made mistakes with the requests.

As in other mass attacks, charitable groups have raised millions of dollars to help the victims in San Bernardino, and some medical providers have given their services free. But survivors of the other attacks have usually not had to deal with workers’ compensation.