You might get customers that you weren't planning on - that's a good thing!

As you start to get unexpected users, how do you think about prioritizing them vs other users - especially in terms of development and prioritization?

Quite an interesting one. Humans are no robots. Behaviour is very unpredictable. Are the "unexpected" clients bringing in more than you originally planned?

I think if you've done your validation and research properly then you should have already identified all the potential customers for your product/business. The only time when you should expect to get unexpected customers is in the last scenario you point out - the pandemic - when things significantly change and so that can change who is looking for your product.

Your customer is like a chameleon, always changing and never revealing their true colors

That's exactly what happened with my startup and I wasn't ready for it. I lost a lot of business because I had the wrong target customer in mind and then when I did get customers who weren't who I expected I didn't know how to manage it. Eventually, I pivoted, but I never got back those potential early sales/customers.