I never worry about Nikon sending any emails for firmware updates. I have a pop up notification to check Nikon site every 6 weeks, takes me 3 min to find out yes or no.
I'm wondering if any other D500 owners we're not notified about the update yet. Maybe they do it in batches?
I have bought 3 Nikon cameras and I don't believe I ever received any notification of updates. I just periodically check the sight and see if they show any updates available for any of them and if there is I just download the updates and install them.
I had problems figuring out how to download it, but I was able to (stupid issue for me). But, anyway, you can download from the Nikon web site without any problems. You don't need an "invitation" from Nikon. So far, seems minor to me as well.
I have 2 Nikons, the first one, a D3100 bought in 2010, and a D500 bought in 2017. I registered both with Nikon on their website as soon as I got them and subscibed to get emails informing me of firmware updates and NEVER got one! Was kind of frustrated that I had to continuously check their download page for any updates. Then low and behold!, last week I actually got my first email (for the D500) advising of a firmware update. I was assuming that maybe things are changing, but apparently NOT based on your question....oh well, I guess I'll just keep on checking the website to be safe.