Complex sentence: Even though only one T-6 was built is is noted as the most tested and studied glider, with complete data published that it has been used a comparative reference glider for evaluating other designs in in-flight comparisons.
Split into simpler sentences: Even though only one T-6 was built is is noted as the most tested and studied glider with complete data published. It has been used extensively as a comparative reference glider for evaluating other designs during in-flight comparisons.