This is what I've found out so far:
The very-famous-celebrities, the reliability of their natal charts is about 75 percent.
The not-very-famous-celebrities, the reliability of their natal charts is about 50 percent.
The non-celebrities, the reliability of their natal charts is about 90 percent.
The very-famous-celebrities, being reserched by more people, so they have more reliable birth data than the not-very-famous-celebrities. The non-celebrities, their birth data was remembered or written, almost zero chart-rectification, more reliable than the celebrities.
What I'm trying to say is, if you have unsure brith data, you highly likely will have an unsure birth chart.
If you know the year, the month, and the day, but you don't know the exact time, you can do it this way: Forget about the houses, only read the stars.
If you don't know your birthday at all, you can do it this way: Forget about yourself, read other people's charts.