Recently received email dates and contents (message within the read area) is different from what I am supposed to be receiving

For some time now, when it is that I receive updated emails from a certain Yahoo discussion group, there are times (but not always) when the date and contents does not correspond with the current date and message title.

As an example of such: A recent email had as its received date "7/24/2014 7:11 PM," but the message contents shows its date as "3/21/2013 12:56 PM", which then also included the contents of the message sent to me that long ago, that is, rather than what I should have received, sent to me on 7/24 (and, by the way, all of which was confirmed from an online visit to the discussion group itself).

Another recent one was dated "7/24/2014 6:43 PM" but then the message date and contents were from "1/28/2013 4:43PM."

Thanks for any help with this, Alan.