Extended trans-sternal thymectomy for myasthenia gravis

Otto reported thymectomy under transverse sternotomy. It currently is not a widely used procedure, however. Jaretzki graded the completeness of removal of thymic tissue as follows: maximal thymectomy 98% to 100%, extended thymectomy 85% to 95%, modified transcervical thymectomy (Cooper) 75% to 80%, VATS thymectomy 80% to 85%, simple trans-sternal thymectomy 70% to 75%, and simple transcervical thymectomy 40% to 50%. The results of each procedure do not always reflect the completeness of removal. The tables show that the most widely accepted procedure is the extended thymectomy, and the results of it are prominent and stable. Why do the results of the maximal thymectomy, however, not exceed those of the extended thymectomy? It is supposed that quantitative increase of removed thymic tissues in the maximal thymectomy might be minimal.