This is a template that I have found useful for adding follow-up observations of the same individual or group of individuals. When you use it, be sure to take away all spaces between the "<" and ">" or it won't work correctly.

Series of observations of the species at the same general location:
< a href="[link to least recent observation]">[date and one of the following additions]< /a>
< a href="[link to most recent observation]">[date and one of the following additions]< /a>

After the date, add one of these.
(same individual)
(same individual or group of individuals)
(not the same individual or group of individuals)

Examples of this format can be found here and here