Board Thread:General Discussion/@comment-26980570-20160320192450/@comment-30438304-20170124113925

Brainifyer wrote: Papyrus doesn't know because he can't see into past timelines.

Sans doesn't EXPICITLY mention Gaster, but he obviously knows about past resets etc. and has quite some scientific knowledge

Also, in the tweet(?) i mentioned he does say the line about Gaster No. Sans doesn't know about past resets. He just knows that the resets are happening and can read your expression.