Board Thread:General Discussion/@comment-33255176-20171006013144/@comment-32182236-20171011233908

Nobody really questions why there's snow in Hotland's stand-They just say Sans was too lazy to clean it up. Perhaps they think Asgore built it, since the CORE leads to the entrance of New Home?

Really, one of the reasons why Sans remembers Gaster is that he only exists BECAUSE of Gaster. That's why to everyone else, Sans and Papyrus just came right in and asserted themselves-They're from the previous timeline-Where Gaster did exist. Papyrus more than likely remembered Gaster at first, but without him ever having worked with Gaster, nor any visual reminders of his existence, or possibly even KNOWING about his disappearance, or the fact that it's easy to forget, he likely didn't even try much to remember, explaining why he could forgot about him.

Also, Gaster is my reason on why Alphys got nervous about how she knows Sans:She knows Sans because they both worked for Gaster, a skeleton that from everyone else's perspective, never existed. So, Sans probably isn't the only knower-Alphys would have to know Gaster too for this to make sense. Remember, Entry 17 with its "What do you two think" still exists... And Alphys had to get the blueprints that she used to extract determination from somewhere... They more than likely were made by Gaster-So she too has something that once belonged to the mystery man.. And her own Entry 17 is mysteriously missing from the True Lab.. Why? Could this too be Alphys keeping a reminder of Gaster? Of the one piece of him that still exists, Gaster's Entry 17? This could be evidence that Alphys too is giving herself reminders of Gaster, and who he was.

...It'd also serve as an answer to the OP.