The ex-Gol 738s are a subset of four among Delta's fleet of 77 738s. Another round of refurb is planned to add AVOD. Do the math: What's the probability of a 738 sub for one's scheduled flight x the probability of an ex-Gol 738 being available in the same location?
It's really quite rare to find monsters under the bed, but small children being what they are...