I think it may have depended on when and where you married as to exactly what happened with the records. An 'original' certificate would be given to the bride and groom. I have several of these and they all have original signatures of the whole congregation.
The instructions given to Quaker meetings after 1753 state that 'a full copy of the certificate (including witness names) should be kept with the registers'. I think it's likely this instruction was complied with in different ways!
I have just looked at Ancestry's records to compare with the original certs I hold. One of them is an exact copy in as much as all the witness names are recorded, but they are all in the same hand. Two others are signed by just a handful of the number of people on my copy, but they are original signatures and on Ancestry's version those few people have included their town of residence and occupation, which are not recorded on my copy. Another two have all the signatures and they are all original and signed in the same order (I think!) as my copy, suggesting the two documents were probably created at the same time.
My comments only relate to pre-1837 records as, though I have two or three more Quaker marriage certs from after 1837, I don't have anything to compare them to.
There's further info here:
https://www.qfhs.co.uk/public_html/r....htm#Registers
with some links to other pages that may tell you more. I haven't looked!