“What’s your number, miss?”
“777.”
“Oh ho ho, but, come on really what is it?”
“It’s 7-7-7.”
“…can I see your ID?”

“What’s your number, miss?”
“777.”
“Oh ho ho, but, come on really what is it?”
“It’s 7-7-7.”
“…can I see your ID?”
I'm guessing they'd actually forbid obvious sequences (all the same digit, sequential digits, whatever) in hopes of avoiding trouble
The number people would imagine equally reasonable constraints for our name systems (“surely they ban duplicate names?”) which we don’t do at all. I think you’re giving them too much credit,