Also according to MA, Ton was also Tongo Rad's name originally, before adding the -go part later. https://memory-alpha.fandom.com/wiki/Tongo_Rad#Background_information So maybe either the name was given to different characters during the writing process, or its (theoretical) association with Sevrin was a mistake, getting mixed up with another character in the story. In the MA article @Tuskin38 referenced above, it also stated that Sevrin was intended to be a Vulcan in an earlier version of the script. (And 'Sevrin' certainly fits with the Vulcan naming conventions they were using at the time.) If "Thomas" is actually a misinterpretation from something else, it's possible that the character only ever had the one name created for him, in keeping with how they named other Vulcans. While "last year" is technically accurate, it's really only been just over six weeks since she was last here. So it doesn't seem out of the realm of possibility that she could return.