On 1st July 1941 following the Soviet force's retreat from Latvia, the Latvian Post issued overprinted Soviet stamps without authorisation from their new German masters. By mid August the German offical post issued German stamps overprinted 'OSTLAND' and the previously overprinted Russian stamps were withdrawn on 31st October 1941.
Michel 1 to 6 "Definitive Soviet Union Stamps"
Issued on 17th to 23rd Jul 1941. Regular definitive Soviet stamps overprinted.