If you run both a Dispatch History Report and an Occurrence Pareto Report, it is likely that these two reports will return different results. This can initially be confusing to the end user. These reports were not designed with the same intended reporting objectives, so the data is different.
The reason the numbers are different is the Occurrence Pareto report only pulls events that were created during the time frame specified. The Dispatch History report pulls a list of all dispatches that were open at any time during the specified dates.
Which report to use depends on what you're looking for. If you want to see the total number of Dispatches that were created during the dates selected, then the Pareto report is the one you want to look at. If you want to see how many Dispatches were open at any time during the time frame selected, then the Dispatch History report is the the one to use.