Does it matter if a child's name was on a checking account when the parent opened it up, as compared to adding the child's name on later?

We separated our fund by me opening my own checking account to continue paying the bills while her funds went into the joint account. Monthly bank statements indicated who made deposits and recorded which ATM card was used as well as who wrote what checks from the joint account.
I did this to protect and ease any lookback, which never came, and to ensure any final check that may have been clawed back would not cause any unnecessary burden on paying the bills.
After her DX of dementia I would use my card to withdraw funds for her use and kept a complete record. I only used my card about four times in a year but I would keep cash on hand for smaller things for Luz. It never exceeded $100.00.

Gabriel Heiser is a good source for information. Could you have maybe misread the quote? The article states:
"If all of the money in an account came from the parent, merely adding a child's name to that account will have no effect for Medicaid purposes because it is not a gift to the child. In this instance, the entire value of the account will still be counted for the purposes of determining the parent's Medicaid eligibility."
I read that to mean the timing of the child's name on the account is not the issue, ownership of the funds is. As worried states, commingled funds are never advised, because the entire value of a jointly named account will always be counted as belonging to the parent by Medicaid.

Wow that article should not have that statement in it because it is not true. It is all dependent on how each state runs their Medicaid program. For some states, it absolutely does matter if the money only came from one name on the account. Even the elder law experts say NOT to commingle funds.

It doesn’t matter how long two names are on the checking account. If it looks like you’ve been given/taken money in the last 5 years (look back period in GA) there will be questions from Medicaid.

I'm not an expert but it may have to do with Medicaid's "look back" policy and preventing people from "hiding" money from the govt. If you can prove the name has always been on the account (for at least more than 5 years), it may protect it. But based on the quote is seems you will need to prove that some portion of the money in that account came from the child. Others who know for sure will give you a more detailed answer.