DNS issues with old time stamps

So I inherited a domain that's 15 years old.  It's DNS has NEVER been scavenged or cleaned up to speak of and it's showing.  I have records with time stamps of tens years ago, five years ago, etc.  I also have multiple A records for DNS names associated with the same IP.  It's generally messy.

In my start to cleaning it up, my first issue is that apparently my PCs and servers are not refreshing properly.  Here's why I say that.

I have a server that is in production and it answers pings.  It of course has a statically assigned IP address.  In DNS, it has a time stamp, which I understand, but the time stamp is seven years old.  I expected that when the server refreshed, the time stamp would update, BUT, have no scavenging settings set, so maybe that's why no refresh.  If I turn on scavenging, I'll lose servers with old time stamps when in reality, they are active.

So, can anyone tell me why I have servers with five year old time stamps that are not refreshed?  I mean I expect the servers to refresh their live status and DNS to change the time stamp.

Thanks!