This is really difficult to know because one cannot tell from looking at a spelling whether or not the parents deliberately were using an unusual spelling, or whether they simply heard a name that they liked without having seen it written down and came up with a spelling they thought was appropriate to the sound they heard, and it turned out to be different from the traditional one.
However, I am sure that deliberate respelling is a phenomenon that is way more than 30 years old. The spelling
Kathryn for Catherine/Katherine is a deliberate respelling that goes back to the 1890s.
There are 177 women named "
Debra" in the index to the 1850 U.S. Census.