Such policies vary from company to company.
Few questions, I want to ask- they did not ask for your documents during your interview? If not during interview, not even before confirming you for a job?
As per my knowledge and experience, these documents are required for verification before confirming the job.
The solution you may have is, you can submit the application letter receipt copy which you have already submitted for duplicate certificates as a proof.
They may consider it and hire you with a term that if you will not be able to submit the documents within stipulated time, you will be terminated.
The rules are different for different companies, so it will be better for your check the same with HR of these companies.
Living & Learning- simultaneous processes!