Based ont he provided description I supposed that you are performing manual ajaxRequest in the onClientSeriesClicked event. If this is your scenarios you could simply check for the ajax eventTarget (request initiator) and make ajaxRequest with some specific arguments. Then on the server AjaxRequest event you could check for a specific argument and perform only the needed logic for one chart. See the help topics below which elaborates on this case:
I hope this helps.
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