I've had the same static ipv4 address for just over 19 months, and have been running an exposed OpenVPN server on an alternative port on that IP for the entire duration. I get no results.

Color me unimpressed that "an army of bots that crawl the entire Internet and stores what it finds along the way" hasn't port scanned every ipv4 address at least once in the span of 19+ months. That is a very long time for a limited address space.

tldr; There is no "army", or that army is armed with pool noodles.