If you filed separate years, then the processing of each year will be separate and will not affect each other. Though, it is likely that the current year will be processed quicker. A prior year filing would have had to be paper filed and they are processed slower.
However, if you just added an old W2 onto your tax return for the current year, then this was a mistake. You cannot add prior year W2s to the current tax year. You need to file each year separately. TurboTax sells prior year software for this purpose. If this was the case, then there will likely be a delay and you will probably receive an IRS notice at some point to clarify the matter.
To preempt any IRS notice, you should amend your current year return (click here for instructions) to remove the prior year W2 and then file the prior year return (click here for information on how to file a prior year return, including links to purchase software).
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