Throughput test

hi all,
I ran the benchmark_tx and rx to measure the throughput ,and I set the
bitrate to 50kbps and samples_per_symbol 5,
I send 200 packets and measure the time it consumend,but i found that
the throughput is larger than 50kbps. can anyone tell me why?
also ,3 packets will always missed on the rx side and 1 incorrect,why?