A lack of historical data about license entitlements is a very common challenge for organizations who are looking to put a new program in place to manage software entitlements. Some tactics to consider to handle this are:

• Ask vendors if they can provide their view of what entitlements you have, or historical records about purchases to fill in gaps in your data. A risk here is that it may alert vendors to your situation, and cause them to start to think about whether you have a compliance issue.
• Refer back to any previous audit outcomes where a license position (entitlements vs consumption) was agreed upon.
• Make an assumption that any licenses which are covered by maintenance were validly purchased at some point in the past. There is an inherent risk here is that the assumption may be invalid.

In terms of actually creating license records in the system to represent entitlements which have an uncertain foundation, you may want to use the license creation wizard which allows you to search for and select between different license models that are available in the PURL for a specific application.

You're on the right track wrt processing a purchase with a SKU that is recognized as only including maintenance: this extends details such as maintenance coverage dates/versions, and does not affect entitlements.