Completed Issues missing from Closed Sprints disrupting Velocity

[Jason Bailey]

My company recently went through a process to standardize our company workflows, issue types, screens, and fields. In the process, it looks like some issues that were completed/done in previous sprints, are showing up in the active sprint, and not being represented as completed in the prior sprint. As you can imagine, this is impacting our velocity.  When I look at the columns on the board, I can see that the issues are mapped correctly, and we don't have any unmapped issues, so I'm not exactly sure what's happening here. If the issues are mapped correctly, what else could cause this type of change? 

[Kevin Johnson]

the velocity chart totally depends upon the story points to show out the results my assumption is if you have missed to give story points for some issue it might be missing from the chart.