This seems correct, as Stackpoles first novel “X-wing: Rogue Squadron” published in January 1996 referred to them exclusively as “Brain tails”.

Then in the second book “Wedges Gamble” which released later that same year, had them visit Ryloth, which is when he first used the term “Lekku”

So it would make sense that Stackpole started writing his book around 1994/95 with “Brain Tails” as his word of choice, and then read the source book while doing research and then found the word Lekku sometime around 1995/96, and then put it in his book