Employers are required to correct errors on Forms W-2 as "quickly as possible" - that gives them a lot of latitude in issuing the corrected form W-2.
"12-18" weeks sounds a bit excessive, however, in the current Covid 19 environment employers are encountering all manner of delays in responding to requests from customer and employees.
The penalty for filing an incorrect W-2 with the Social Security Administration increases over time. To avoid penalties, a Form W-2c is generally required within 30 days of becoming aware of an error. As the "customer", however, there is very little you can do to influence the process.
