Why does not directly read encoded data from output buffer?

Gaming and Visualization Technologies Video Processing & Optical Flow
1

In nvidia nvenc samples, a variable m_nOutputDelay is used. What does it mean? The encoder output encoded data to buffer m_iToSend%m_nEncoderBuffer.
picParams.outputBitstream = m_vBitstreamOutputBuffer[m_iToSend % m_nEncoderBuffer];

But when it read data, it is below:
unsigned i = 0;
int iEnd = bOutputDelay ? m_iToSend - m_nOutputDelay : m_iToSend;
for (; m_iGot < iEnd; m_iGot++)
{
WaitForCompletionEvent(m_iGot % m_nEncoderBuffer);
NV_ENC_LOCK_BITSTREAM lockBitstreamData = { NV_ENC_LOCK_BITSTREAM_VER };
lockBitstreamData.outputBitstream = vOutputBuffer[m_iGot % m_nEncoderBuffer];
lockBitstreamData.doNotWait = true;
NVENC_API_CALL(m_nvenc.nvEncLockBitstream(m_hEncoder, &lockBitstreamData));

    uint8_t *pData = (uint8_t *)lockBitstreamData.bitstreamBufferPtr;
if (vPacket.size() < i + 1)
{
	vPacket.push_back(std::vector<uint8_t>());
}
vPacket[i].clear();
vPacket[i].insert(vPacket[i].end(), &pData[0], &pData[lockBitstreamData.bitstreamSizeInBytes]);
i++;

NVENC_API_CALL(m_nvenc.nvEncUnlockBitstream(m_hEncoder, lockBitstreamData.outputBitstream));

if (m_vMappedInputBuffers[m_iGot % m_nEncoderBuffer])
{
	NVENC_API_CALL(m_nvenc.nvEncUnmapInputResource(m_hEncoder, m_vMappedInputBuffers[m_iGot % m_nEncoderBuffer]));
	m_vMappedInputBuffers[m_iGot % m_nEncoderBuffer] = nullptr;
}

if (m_bMotionEstimationOnly && m_vMappedRefBuffers[m_iGot % m_nEncoderBuffer])
{
	NVENC_API_CALL(m_nvenc.nvEncUnmapInputResource(m_hEncoder, m_vMappedRefBuffers[m_iGot % m_nEncoderBuffer]));
	m_vMappedRefBuffers[m_iGot % m_nEncoderBuffer] = nullptr;
}

}

Why it is not directly read from output buffer m_iToSend % m_nEncoderBuffer