Incorrect asset depreciation

We have an issue with depreciation of assets. The assets were added with a life of 50 years or 600 months. After a several years of depreciation, we noticed that the monthly depreciation amounts were incorrect, calculating based on 565 months instead of 600. I believe what caused the issue is that we didn't have our calendars built out in the future far enough when we initially added the assets. Now that we discovered the discrepancies in depreciation amounts, we need to now the best way to fix it. We have built our calendars out, but the assets are still