HI Macjack,
My "To" list of numbers includes ones from my Carrier from SMS items they have sent me that appear in Messages having been synced to the Mac.
There are several numbers as they send different types of messages, Alert, Notifications, offers and so forth from different ones.
These are not listed in Mail.
Messages used to have a Recent Chats list in the File Menu but it has disappeared.
There was a separate .plist for this (com.apple.iChat.LSSharedFileList.plist) but this no longer works if it has not been removed and is not there if you have had a later OS in the first place.
The List of Recent Chats is now in com.apple.ichat.plist but does not list the items I was looking for.
There does not seem to be the equivalent of the Mail Previous Recipients list.
8:00 pm Thursday; November 26, 2015
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad