This is my guess: the more recent isotope location information we were told about probably came from the hair and nails. This was the approximate 7 months before they died. This may be all the hair/nail info revealed, based on the lengths.
The longer term results, like investigators stating there was a high probability Marlyse grew up on the east coast, most likely came from bone and teeth.
Of note: TX doesn't show up at all on either isotope result maps, so if the 4 were there, it wasn't long enough to leave a trace, as certain parts of TX have very distinct/exclusive water isotopes. (I researched this for the Marcia King case before she was ID'd).