According to the industry sources, the leading 20 grain exporters recently received (highly informal!) grain "export quotas" for the rest of 2018/19.
the "quotas" are based on the historical companies' market shares in the first half of the season. The possible assumption is that that total remaining export volume is about 12 mmt of all grains, subject to further possible corrections during the rest of the season.
the rest of companies, those who are out of "magnificient 20" are, apparently, out of "quota" system.
Info from IKAR, DR