A degree certificate and a transcript of studies is usually presented at the convocation ceremony for those students able to attend; thus the degree certificate and convocation certificate are one and the same. For those who cannot attend, the certificate (call it what you will) and the transcript of marks is either mailed out or picked up at the college (university) office.
This is to the best of my knowledge. If some colleges/universities have two separate certificates, I am not aware of it.
Ray