This does happen all the time in the US - I was once a carpenter and did it all the time.
But, there is really no one mechanism for planning commissions and building offices to discover such changes. And often, there are simply no permit or planning regulations in effect in the particular area. As such, it all depends on the location and local laws; and if the building is commercial and open to the pubic, or a private residence.
For commercial buildings, the laws and enforcement are much more strict. When a commercial builder pulls a building permit or submits plans to a zoning commission for approval, there are records as to what has been done with the commercial property, and preinspections take place beforehand, in order to detect previous unpermitted work. And the preinspection also takes into account any new laws, re: asbestos remediation, that have taken effect since the last work on the property. Commercial builders are mostly very careful to be law-abiding, as their licenses depend on it. Cities are very careful with regulating commercial work, due to liability.
For private residences, there is little of this oversight. Unless there is a fire and the investigation finds unapproved and unpermitted work, or there is a structural failure that brings an investigation, many homeowners do extensive work to their houses off-permit and get away with it.
There is simply no central record mechanism for tracking changes to private residences at the local level. If there was, there would have already been a tea party-type insurrection in the US due to infringement of personal liberties and property.
Employees of building commissions and permit offices do keep an eye out for off-permit work. And if the owners of a private residence do get caught, they have to apply for a permit and remediate the work. But significant work - like additions, gut-outs, second floors and basements - routinely gets done with no approvals and no after-the-fact discovery.
One of the only times private residence off-permit work may come to light - other than the reasons above - is when a homeowner gets insurance coverage on the new work. The insurance company may want verification that the work was done legally and has the proper electrical, plumbing and structural inspections. But I doubt the insurance company would report the owner; the company would simply cancel the policy, due no doubt to a contract clause saying they can cancel the policy due to changes to the property done in an illegal manner.
And, this kind of work can come to light when the house is sold and an inspection is done by the buyer by one of the many "home inspection" businesses out there; these casual inspections can be optional or required by local laws and realtors. But again, changes may simply not be reported to a building or planning commission; there is no benefit unless something drastically wrong is discovered and the buyers/sellers knows about it in their contract.
Now, many areas of the US - I'd say the majority of the private land area in the US - simply have few to no building codes or permit laws (or zoning laws) being outside of city limits. And many counties have very minimal laws because they are outside city limits and have very few regulations of their own.
In many locations, I can build or renovate any kind of a horror story of a shack and live in it and sell it to whoever buys it. With no oversight of any kind, before or after.
It's all location, location, location. And the local laws.
And I do know of people who dug out their own basements and poured concrete without building permits. But, I don't recommend anyone do it themselves.