none really, as i found out.
if you reflash the new ones, then you get the latest. But if you had the prior version and had updated any in the play store since then, then you essentially have the latest.
I kept the 2013 one to replace the older one for when doing a new clean flash in the future, you know, for MMuzzy 5.0
That's a good plan to replace the older one with the new one for reflashing. I've done that also. It's worth it even to eliminate that FC of Google Now due to Search not being updated. That was annoying. MMuzzy 5.0. Thanks for the smile on that one. It makes me think of the old Mustangs with the honkin' engines in them.
I have high hopes for Android GT this year.