RE: Creating a replica with same universal id and Note ID Willy Lorenzo 4.Feb.13 02:26 PM Lotus Notes Applications Development All ReleasesAll Platforms
"This is why applications should never use the NoteId. They are not a stable identifier. You should always assume that they can and will change. If you need a stable identifier, use the UNID."
And for an even more stable identifier, simply create your own identifier. UNID can change if there's a replication conflict.
After doing this for a long time I've found that it's best to never use any of the system fields in one's application. If you need a piece of data, just create your own. I don't even use the response hierarchy any more (another structure that gets damaged from a replication conflict.)