There really is NOT any serious accounting for reserves. Someone provides a seemingly objective estimate of what is thought to be available in a particular area. A casual inventory control analyst would then expect the next year’s reserves to reflection any addition of new gas created and subtraction of gas extracted. Gas extracted would be the sum of gas produced and gas lost or wasted or burned off. Usually, what in seen is that reserves are reported as the same for years and years. When it comes to storage tanks and pipelines the amount of natural gas stored or in transit is usually ignored. In its simplest form production plus imports should roughly equal consumption plus exports. There has been no real effort to distinguish between inventory passing through and inventory to be consumed: for Germany, for example,  if natural gas comes from a pipeline through Poland, regardless of whether the gas is destined for German consumption or is simply headed to Denmark or Belgium, that gas is an import. Likewise, the natural gas than continues on Denmark or Belgium is an export. Here are some historical figures for Indonesia. Note that no (zero) imports were reported