a. On three occasions, three firemen came to our bar.
b. Three times, three firemen came to our bar.
c. Three firemen came to our bar on three occasions.
d. Three firemen came to our bar three times.
In which cases:
we are sure that three firemen came together every time
it is possible that one came on each occasion. Three fireman in all and three occasions in all. One fireman on every occasion
We know that there were three firemen in all and each came three times, but they might on some occasions have come together or two of them might have come together on some occasions etc.