The paperwork really matters
There are a number of compliance tests and the issue is that the place doing the testing can be audited.
In the UK, audits and accreditation are performed by UKAS.
If a company did this with goods for sale in the EU (which require a CE marking) they would be in very big trouble. Although CE is a self certification system you are required to provide compliance evidence if it is demanded by the relevant authorities.
Non compliance can get products removed from the market although manufacturers are usually given a chance to prove compliance; a lot of them might not because the process is expensive.
The facilities in China are not necessarily audited to the satisfaction of other countries which is possibly one of the reasons China is not a signatory to the agreement.
Not being a signatory means that the paperwork cannot be accepted because the quality of the actual work done cannot be shown to be adequate,