The fact that people question the just Mary thing surprises me. Do you suppose they want to be sure you aren't trying to simplify it for them? As in "I'll just tell people to call me Mary since they flub various longer versions" Like they wasnt to be sure "Sue" is really just "Sue" and not giving up over Susan/Suzanne frustration?
Sadly, it doesn't surprise me at all.
In real life, my name is Mary. Middle name is Ann. So it looks like Mary Ann.
Everyone reading my name from a list calls me Maryann. You don't automatically call Elizabeth Ann by both names, do you? or Catherine Ann, or Lulinda Ann or Barbara Ann?
Nope. Just the Mary Anns of the world. When I correct people, "Please call me Mary," they get all huffy and protest that my name is Maryann. I even had a teacher, who had the correct spelling on her class list, write my name as Marianne.
It's to the point where I do not write my middle name out unless it is absolutely necessary--like on a legal document, or my driver's license. I just use the initial.
So I can easily see, from my experience on the other side of the issue, why someone with a name like "Mary" gets questioned about it a lot.
As for my last name, I am now the proud possessor of a library card with my last name misspelled on it. You see, there are two different ways of spelling my last name. The nice woman who was giving me my library card has the same last name as me, but with the different spelling. Guess what she did? Yep, she used her spelling and not mine on the card.
We both got a good chuckle out of that. It will get changed next week, when the only person with authority to change the computer records is back at work. (They still let me check out books, so there's no reason for me to be upset. Perfectly understandable little mistake.)