Excel adding "__2" to the end of sheet names

[ExcelAtEverything]

It may be just a coincidence (or maybe it's just that I'm only just now noticing), but it seems that ever since I started converting my ranges to tables, I keep noticing that my formulas are changing the sheet name by adding underscores and a number to the end of the sheet names.. For instance if the sheet name is "Annual_Plan_Numbers", it shows up in formulas as "Annual_Plan_Numbers__2". Also, at other times I notice that the sheet name (on the tab itself) will change to "Annual Plan Numbers (1)", even if there are no identiacally named sheets. What is the reason for this, is there something I need to do to prevent it, and do I need to go back in and manually edit all of them by deleting this added suffix?

Thanks!