Hello,
On some pages where a flag is preferable (i.e. in lists, where a missing flag would break alignment), issuers which don't have a flag re-use the flag of their parent issuer. That's why you see the flag of German states in the search results for Mülhausen. On other pages, flags are optional: no flag is displayed if Numista doesn't have a flag for the specific issuer. That's why you see no flag on the coin page for that coin from Mümhausen.