You should at first consult the people/companies who undertook the works and try to get the issue resolved. Lost, miss-placed or un-received paperwork can cost time and money in chasing around retrieving documents.
If it isn’t possible to get historic or non-received documents, and you’re trying to sell a property, your solicitors may get you to pay for an ‘Indemnity Insurance’, which sort of covers the ‘non-compliance’ rule. How-ever, if a ‘third party’ highlights an issue within the property (say, an Electrician has noted a dangerous installation) the indemnity insurance would be void for that part.
It’s always beneficial to get the correct Certification and documents with your new installation and to save the documents with cert0n after you’ve received them.