Leaving aside variations in the details that the parties gave to the person performing the ceremony, errors on marriage certificates are quite common. If it is a church marriage (and most were until well into the 20th century), the difference is often between the original entries in the the church registers (two were made at the time of the marriage) and the copy that was sent to the GRO at the end of the quarter (the Quarterly Returns).
Some members of the clergy were simply not very good at making accurate copies, so it is always a good idea to look at the church register entry for a marriage when you have obtained a certificate through the GRO. Sometime the differences are minor, and don't make any significant difference - middle initial instead of middle name, for example. Sometimes it is much worse, such as a completely wrong name for one of the parties or one of the fathers. It is becoming easier to spot these with the growth of the wonderful UKBMD local projects, and I suspect that there may be even more than we once thought.
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