Deltarune’s relationship, timeline-wise, to Undertale is quite perplexing. In this world, Asriel was never killed because Chara is off somewhere else, presumably living a different life than the one she lived in Undertale, which caused her to attempt suicide (leading to her discovery of the monsters under Mt. Ebbot). This means that the other humans never fell either, and may not even be born yet depending on their ages, and the dubious amount of time that Asriel spent either dead or as Flowey before the end of the game. This means that the events of the game actually happen earlier than Undertale’s do, at least in relation to the time of birth of their respective Asriels. This is also evidenced by the fact that, since Asriel was not killed, (allowing them all to age further) the elder Dreemurrs appear a tad older than they did in Undertale. However, we must also take into account that magic doesn’t seem to exist in deltarune, another definite difference between the two games. Not once in Hometown, to my recollection, does any monster refer to SOULs, or magic, or Determination, or stats, or anything. The only time we can see these in this world is in the Dark World, which may or may not have been in part created by Kris and Azzy. So maybe that has something to do with Gerson’s death.