The perspective will not categorize historical costs in this situation.

Big Query Line Item will operate differently compared to the perspective built on the tag for other cloud platforms like AWS/Azure.
 
In the case of AWS and Azure, the billing files include a resource ID, allowing the tag's backlink to function.  This results in the allocation of resources within the perspective group, even for historical months.
 
However, the situation diverges with GCP.  The bill files lack a specific resource or asset ID so to achieve the goal of effective cost categorization, the platform generates a synthetic asset ID derived from various fields within the bill file, such as SKU and labels, etc.

Historical data will appear in the platform from the date Labels began appearing in the bill files.

Example: if the inclusion of Labels commenced on August 7th, and considering that the field label significantly contributes to the formation of synthetic asset IDs, the historical costs won't be categorized according to the Perspective Group.  Instead, the categorization will be effective from August 7th onward.