A missed period is probably one of the most reliable signs of pregnancy (but pregnancy isn't always the reason for a missed period). (verywellfamily.com)
The most reliable sign of teething is when you see a tooth poking through, but you do not have to wait for this to happen because there are several other reliable symptoms. (momdiscuss.com)
It mentions «physical feeling» and «data», usually reliable signs that this is D or later. (religion-online.org)