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Solution: Juxtapose the language combination used for the project and the one from the import file, and check if they are consistent.
TM matches from an older project with similar content are not appearing
Sometimes, while working in XTM Workbench within the framework of a particular project, you might experience lack of TM matches with similar content that shall supposedly come from an older project.
Solution: There are a couple reasons that might stand behind this issue:
The TM matches from the old project are set as not approved and you do not allow using not approved translation memory in your current project.
The new project was created before the TM entries were created, and you did not open XTM Workbench in the Edit Mode yet, so a match update was not triggered.
You are using a TM penalty profile that penalizes matches from the old project.
The old project was created under a different customer that the new project does not have access to.
The language combination is not exactly the same. It perhaps uses different variants.