Just a bit of info to help with the checking. I looked at the X/AS summaries of all the pokes I Banked from various games & this is what I found. This is all from stuff that I know is 100% legit, because I either caught it myself or got it from the event myself.
When looking at 6th gen games, summaries will say:
3rd gen LG/FR says: Seems to have traveled across both time & space in order to reach the Kalos region from the Kanto region.
3rd gen R/S/E says: Seems to have traveled across both time & space in order to reach the Kalos region from the Hoenn region.
3rd gen MYSTRY Mew says: A fateful encounter seems to have led it across space & time to reach the Kalos region from the Hoen region. No ribbon.
3rd gen WISHMKR Jirachi says: Seems to have traveled across both time & space in order to reach the Kalos region from the Hoenn region. No ribbon.
3rd gen Colosseum (Gamecube) says: Seems to have traveled across both time & space in order to reach the Kalos region from a distant land. Has National ribbon.
3rd gen XD (Gamecube) says: A fateful encounter seems to have led it across space & time to reach the Kalos region from a distant land. Has National ribbon.
4th gen D/P/Pt says: Seems to have traveled across both time & space in order to reach the Kalos region from the Sinnoh region.
4th gen HG/SS says: Seems to have traveled across both time & space in order to reach the Kalos region from the Johto region.
4th gen D/P/Pt event says: A fateful encounter seems to have led it across space & time to reach the Kalos region from the Sinnoh region.
4th gen HG/SS event says: A fateful encounter seems to have led it across space & time to reach the Kalos region from the Johto region.
5th gen B/W/B2/W2 says: Seems to have traveled across both time & space in order to reach the Kalos region from the Unova region.
5th gen B/W/B2/W2 event says: A fateful encounter seems to have led it across space & time to reach the Kalos region from the Unova region.