Many airlines allow their tickets to be combined in various ways. One of those is end-on-end which means that you for example fly NYC-LON on AA using fare X and then continue on OK to PRG using fare Y, all on the same ticket. KLM's fares are notorious in that they do not allow this.

In your case you have nothing to worry about though. This rule only applies when you have more than one fare on the same ticket.