Panalty provision for voilation of rule 4a(1)

My company got the verious service like man power, vehicle hiring, work contract etc from verious service provider. As per Rule 4A(1) The invoice / challan / bill should contain following details-

1 Name, Address and registration number of person providing taxable service

2 ----------------

3 -----------------

I want to know whether we are liable to pay service tax if service provide not mention the Registration Number on the Invoice however service provider submit the registration certificate to the company.

Please provide your valuable input on the above querry as soon as possible in details