savings from before 1-1-2024 are indeed not taxable, savings you got after 1-1-2024 are taxable, this to prevent rich Thai earning money abroad to leave that money for some time abroad and then get it in tax-free.
But they already want to change this law to make it attractive to get that money in the country.
But for now it means that all money you bring in, regardless what kind of money, is taxable unless you can prove you did already have that money before 1-1-2024.
When you did not have to pay the fee again, your application was not rejected, they only asked for additioanal info, once rejected means application ended and you have to do new application.
People worrying about being questioned, most likely do not comply with visa rules or have to hide something else, otherwise questioning just is no issue at all.
The fact you are not questioned will not reassure them because there always is a chance to get questioned.