How do you verify that they are true?

It's quite well known that the vikings bathed once a week or more, that's 750-1100 AD. Many sources tell of the rituals of bathing, and the day of the bath was called bath-day, in norse laugar-dag (lauga= to bathe). That evolved to the modern "laurdag" or "lørdag" still used today as the only name for Saturday.

The custom of carrying flowers on your wedding day probably has more to do with decoration than scent - how many flowers do you know that would overpower say one week of body odour? Let alone a month?

The phrase "dead ringer" is by some linguists explained thus: The word "dead" can, among other things, mean "accurate" or "total". Think "dead tired" or "dead on target". "Ring" is used a lot to mean "thought" or "connotation". So a "dead ringer" gives you connotations of another person that are very realistic.

It's very interesting to dig up the likely and probable explanations for such phrases and phenomena, but the chain mails that pop up, however cute and funny, are usually only cute and funny.

Oh, and the coffin rots many years before the corpse. I know this from my experience as an ex-gravedigger...