Thanks zizi for your help thus far. I'm not sure if I'm allowed to provide specific names/ip's, so I'll do my best.
I ran nslookup for the node from the polling machine, using the polling ip, and I'm getting "*** (domain controller name) can't find (ip): Non-existent domain"
The full name of the node is core.****-llc.com, whereas **** is our internal website name.
I also ran snmpwalk.exe for the ip, and I found several ip's for OID(1.3.6.1.2.1.4.20.1.2) which don't agree 100% with NPM. I assume it's because of the nslookup error, right? I'll check with our DNS administrator to see if he has any ideas.
Per DNS admin, this node is not in DNS. Below are the IPs found in SNMPWalk.exe. It appears NPM does match the SNMP info.
NPM IPAM SNMP subnet
.4 .4 found B
missing .7 B
.9 (ping fails) missing found B
.10 missing/fixed found A - IP now shows up in IPAM after adding the subnet
.17 .17 found B - primary polling ip in NPM
missing .24 B
.25 .25 found B
missing .31 B
.186 (ping fails) listed under system name SW01 found C
n/a n/a .51 (on first line; from a subnet not in either module) D