Matches not in TM when connecting to same TM for Follow-up project

 This is a general issue I have often experienced in the past with Studio 2011 (but I assume this won't be different with my brand-new Studio 2017: I often tried to use my main European Union TM in combination with a project TM sent by the customer in a project package. Under Project Settings I chose and activated these two TMs and performed the translation. However, when I received a second follow-up project (again in a package with project TM) I of course wanted to use the matches from the previous project so I again chose my main basic TM thinking the previous text was now present as matches in this TM. However, I never got any matches (and when I performed a concordance search it turned out that the text was not in the TM indeed – even though the file manager showed that the TM had been in use und safed recently). So I had to reconstruct what I had translated before from memory or by going back to the older text and do copy and paste. What can be the problem here?