that's for the simple reason that until the 1840's most marriage entries were required to merely stated parish of residence of the parties, their existing marital status and if they were of full age (the last two usually only explicit if a widow or under age) + the names of two or more witnesses - the names + occupations of the father only became required in the 1840s tho some vicars (generally in the more rural parishes) did add additional information into the register tho usually it seems to distinguish between those sharing common names.