first step of several
This is a very good first step to challange Microsoft on those FAT patents.
Once sufficient information is accumulated (and Microsoft refuses to promise not to impose them again against Linux or other open source projects) it is possible to file for a declaratory judgment that the patents in question are not enforceable.
Otherwise Microsoft will just pick off one ISV after another forcing one at a time to either drop using the FAT file format or pay patent royalties. Or, even worse, come to some vague agreement like Tom Tom that Microsoft will just use to threaten everyone else.
One at a time, vendors may be venerable even if the various open source organizations agree to defend the use of the open code. Practically speaking, smaller companies can not afford to delay product development or even marketing while a few worthless patents are litigated.
Certainly Tom Tom was more concerned with the non-FAT patents. But, no doubt, Microsoft will lie and tell everyone that the FAT patents were the ones collecting those royalties.
So, yes, it is important to gather together the necessary evidence of prior use and bring a law suit against Microsoft if they do not promise to hold off.