Can I use an ampersand in my apple login password?

I spent hours on the phone with Apple support and at the Genius Bar trying to debug why I could not log my iphone SE into my apple account . I had set up the account using my PC W10 and had successfully logged out and in several times. But when I tried on my Ipad and Iphone it failed. Turned out that the ampersand & was not recognized from the apple products , but it was using the original W10 device. I changed the password (from my W10 PC) to not use the & and suddenly all was fine.

1. Why would Apple allow the character to be accepted in the first place?
2. Why is there no one at Apple support that knows to ask about characters that are not allowed in Password?