The processing code indicates that the return made it through the general processing phase of the processing unit at the IRS and the data has been recorded in the IRS database.
It doesn't guarantee that the return will not be subject to review at a later date or mean anything other than the return has be recorded in the system. It is just a "timestamp" of sorts for the return.
There isn't any notation on a transcript that will indicate that the IRS considers a return to be complete, correct, or "approved" - that sort of notation doesn't exist.
All tax returns are subject to additional review within the statute of limitations for that return which is generally the later of three years from the date the return is filed or two years after the tax is paid.
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