Timing of when to add/update a custom depreciation method to ensure the correct assets are impacted

Summary:

Looking for guidance on the timing of when to add/update a custom depreciation method to ensure only the intended assets have the new depreciation method applied.

Content (required):

The fixed asset functional lead in conjunction with our IT team configured a new custom depreciation method (bonus depreciation) that they wanted to start at the beginning of our fiscal year (July 1st) and everything tested in the lower environment correctly. When moved to Production, they made sure to migrate after 7/1 however there were assets with in service dates prior to 7/1 that had the new bonus depreciation applied. As I was discussing with the functional lead when trying to determine what might be the cause of this mistake, I had asked if the fixed assets module was closed