In my experience, the counts shown in FTM for "marriages" are meaningless ;-) I have tried and tried to make sense of what they are counting and I cannot reconcile their counts with the actual data ;-) Indeed, I had to write my own program to read the GEDCOM output from FTM to see what was really going on.
Example - my primary FTM DB. FTM says that I have 1402 people and 400 "marriages". In actual fact, the following is true - based on the GEDCOM output:
Number of Individuals: 1402
Number of Families: 420
Number of Invalid Families: 7
Invalid Family: @F47@
Invalid Family: @F48@
Invalid Family: @F49@
Invalid Family: @F51@
Invalid Family: @F308@
Invalid Family: @F309@
Invalid Family: @F333@
Invalid Family (Husband or Wife and no children): @F47@ - -
Invalid Family (Husband or Wife and no children): @F48@ - -
Invalid Family (Husband or Wife and no children): @F49@ - -
Invalid Family (Husband or Wife and no children): @F51@ - -
Invalid Family (Husband or Wife and no children): @F308@ - -
Invalid Family (Husband or Wife and no children): @F309@ - -
Invalid Family (Husband or Wife and no children): @F333@ - -
Valid Families with Marriage and Source: 353
Valid Families with No Marriage: 55
Valid Families with a Marriage and no Source: 5
Invalid Families with Marriage: 5
Invalid Families with No Marriage: 2
An invalid family is a family with no "husband" AND no "wife" ;-) It is a phantom left in the FTM DB when records are deleted in the wrong order. Of my 7 invalid families, 5 of them have a marriage event ;-)
However, even taking this information into account - I cannot total any of the values above and get the answer "400" ;-)
You can probably assume that RM counts are correct. PS I reported all these issues to FTM over a year ago - no fix has ever been provided - nor any explanation about what their "marriage" count means ...