Stepped up basis of stock following death of Joint Owner

[dms111]

I own several publicly traded stocks that my parents bought for me when I was a child.  Originally, they were owned via a UGM account.  But when I became an adult, the stock was transferred to a joint account WROS owned jointly by me and my mother (my father died many years ago).  My mother died in 2020.  Question:  Do I get a stepped up basis in 100% of the stock since 100% of the purchase price was paid by my parents?  

Thanks!

[JohnB5677]

When you sell the shares, how you will be taxed, half of the investment’s tax basis was stepped up when your mother died.

That means when you sell, the capital gains or losses on your half of the investment will be based on the stock’s value when you originally purchased it, but the basis of your mother's share will be based on its value at the time of her death.

[dms111]

I thought that was true only if the joint owners are spouses.  Otherwise, I think the basis is based on how much each joint owner contributed to ownership.  In this case, my parents paid 100% of the purchase price so I think I would get a stepped up basis in 100% of the value of the stock at my mom's death.  Is that not correct?