pcap_sendpacket and pcap_sendqueue_transmit packet drops

Both pcap_sendpacket and pcap_sendqueue_transmit return status (the latter via total number of bytes sent which can be compared to sendqueue->len to verify if all packets were indeed sent).

Is this just the system call status or is there a guarantee that the packets did make it out of the NIC?

If there is no guarantee is there a way to get any drop stats out of the Windows kernel/system to confirm this?

In my tests, I have two pcap_t handles A1 and A2 for the same adapter A. I call pcap_sendqueue_transmit on A1 and am able to 'capture' these sent packets on A2. However, the number of packets captured on A2 is sometimes less than the number of packets sent on A1 - especially at high send rates. I would have expected these counts to be equal. This leads me to suspect that there is some packet drop somewhere.

npcap version: 1.10

Start with the pcap_sendpacket and pcap_sendqueue_transmit entry points and compare their reported status with the packet counts observed through handles A1 and A2. Reproduce the high-rate Windows case and determine whether the behavior reflects documented transmission semantics or requires kernel drop statistics; done means documenting the guarantee and a supported way to verify losses, if one exists.