QB Issue Resolution:

the date on a supplier invoice, your bill, is for his accounting, your accounting should use the date you received the bill.

But yes if you back date a bill it will affect the previous periods

Resolution for Issue 'can post supplier invoices which date is the past into the current period and not impact the past accounting figure?' available: Yes (Solved).
Source: Intuit Community forum.

can post supplier invoices which date is the past into the current period and not impact the past accounting figure?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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