Insurance is bought per risk, and the risks do not overlap. A business with several policies can still have a gap, because each one is written to cover a particular kind of harm.
The core policies
General liability — injury to other people and damage to their property caused by the business. The baseline policy, and the one most commonly required by customers.
Workers compensation — injury to employees at work. Mandatory in most places from the first employee, and priced by trade.
Commercial auto — vehicles used for business. A personal policy generally excludes business use.
Property — the premises, equipment and stock owned by the business.
Business interruption — the income lost while the business cannot trade after covered damage. Sold alongside property and frequently omitted.
The ones bought for a specific exposure
Professional liability — being wrong rather than breaking something. For advice, design and specification.
Cyber liability — a data breach or compromised system.
Employment practices liability — claims by employees about how they were treated.
Employee dishonesty — theft by staff, which the standard policies exclude. See fraud prevention.
Tools and equipment — usually excluded from both the auto and the property policy while in transit. See tools and small equipment.
Umbrella — a further limit above the liability policies. It extends limits and does not widen scope.
Not insurance, though bought alongside it
Bonding guarantees performance to a customer rather than protecting the business. Frequently a licensing or contract requirement.
Where gaps appear
Between policies rather than within them. Tools in a van, a subcontractor without their own cover, an employee driving a personal vehicle on business, a data breach with no physical damage.
Each is a case where the business holds insurance and the specific loss falls outside all of it.
Certificates from others
A subcontractor's coverage is what protects the business from their work. Collected once and never re-checked, it lapses and nobody knows until a claim.