HI,
I will rephrase Eric's question again.
On your Mac in the Messages App you have an Apple ID set up as the iMessages ID, correct ?
On your iPad in Settings > Messages > Receive At/Send from you have the same Apple ID listed ?
If this is the case and both the Mac and the iPad are On and connected suitably to the Internet then any iMessages sent from the Mac will appear on the iPad and any iMessages sent from the iPad will appear on the Mac version.
If the Mac Is Off Line when you send iMessages from the iPad then it should play "Catch-up" once the Messages App is started again.
If you are on trip with the iPad and do not have access to the computer then there is a limit of how many days the iMessages Servers will Sync when the Mac version is On line again.
The same would be true if you used the Mac version for a while and the iPad was Not On line for a few days.
Basically you should have iMessages appear on both devices if both are used fairly frequently.
You will not get the iMessages Server to sync any iMessages before the date you linked the iPad and Mac to the same iMessages account (depending on which you did first).
It would be possible to have both devices with their own Apple ID uses in iMessages.
One of these Apple IDs (which is normally an email) could then be used as a Additional email Received At and Send from ID.
However it is then very difficult to stop the other device also listing the other Apple ID and ending up with 2 Apple IDs integrated over both devices when you were aiming to do only one.
I have done this with two iPhones.
iCloud IDs can be used separately in iMessages on each device. However something about the IDs is recognised by the Mac version and it tries to add the email and second iPhone Number.
Due to losing WiFi networks and sometimes Data service as well then iMessages will consider the iPhone to be re-registering and send the info to the Mac version again when the iPhone reconnects to the internet.
Summary.
By adding the Apple ID to the iPad (or to the Mac version after doing it on the iPad) and getting the pop up to say the other device is using the Apple ID you create a link between the two.
From this point in time the two devices will sync the messages sent from each other.
It will not sync older Messages that were sent by either device (on an iPhone you could be sending messages via the iPhone Number before linking in the Apple ID).
There limits to how long a device can be Off Line and the iMessages servers "catch up" old iMessages to the that device.
You could have missing Chats or parts of chats.
If you have removed chats from the iPad you cannot use the version on the Mac to "recreate" it on the iPad.
8:28 pm Monday; July 29, 2013
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.4)
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
"Limit the Logs to the Bits above Binary Images." No, Seriously
