The syntax-troubled sentence that George corrected reads like this:
Gennifer Flowers claimed that she had a 12-year relationship with Bill Clinton in 1992.
Following is Georg’s correct assessment of the problem with this sentence, and his guess at what the author intended to say:
The writer states that within the year of 1992, Gennifer Flowers managed to fit in a 12-year relationship with Bill Clinton. The writer probably intends to say that in 1992 Gennifer Flowers claimed to have been in a relationship with Bill Clinton for the past twelve years.
The only thing I’d change is the phrase “for the past twelve years,” because the original sentence doesn’t state that. If the claimed twelve-year relationship were on-again-off-again, the twelve years would have accumulated over a longer period of time.
I’d keep it as close as possible to the original statement, and put it like this:
In 1992, Gennifer Flowers claimed to have been in a relationship with Bill Clinton for twelve years.
Thank you, Georg!