Assuming neither of the couple being married was trying to undergo bigamy, or declared their age to be more than it was (i.e. under whatever the legal date for a marriage was at that time) then I would assume that they were marrying in good faith that everything was as it should be, and that therefore in the sight of God, the marriage would be legal.
I know of several cases when the local vicar doesn't do a wedding when he might be expected to .... holiday of the local vicar ? Illness ? Family connection ? One of the couple coming from and having close family ties with another parish, and so that vicar did the ceremony ?
A lay minister cannot perform a wedding, which is a legal ceremony, whether in church or registry office or nowadays in a licensed venue such as a hotel ... so the celebrant has to be a registrar. A funeral can be done by anyone, and baptisms are sometimes done by lay people such as a nurse in an emergency. Funerals and baptisms are not legal ceremonies.
