With regards to build hours on a town, they are stored per town and not as part of character data. The devs could also have set up something to search every town on the world to see if you had build hours against any of them. They probably just didn't think it was worth it - and I'd say that they were probably right.
I completely agree it probably wouldn't be worthwhile to do it THAT WAY.
What I was thinking of, was if someone goes back to their old town & town hall shows they have over say 100 hours of construction [any number NOT easy to obtain], I would like to think the mods could than give your account the medal(s) you otherwise would have gotten.
Since it would be town hall records, NO cheating involved and by putting in a minimum number, I don't think the mods would get swamped with requests [since it is a one time thing]. If they wanted to add a player for minimum X months limit, too that would be fine, also.
Or...and this is just an idea...you could decide not to bother.
There's no need to get achievements. If you don't have one then you aren't a worse player.
It's not unfair anyhow. Everyone is in the same boat.
The problem is we are NOT ALL in the same boat, if you just joined a couple weeks ago, like in world 10, as an example, practically all your time would have counted and YOU could, if you choose, end up with any super high awards there are, while the ones that have toiled & labored, since the earlier world's were founded would get nothing, so I don't believe it is fair to say we are all in the same boat.
Perhaps this is so all the soon to be "stuck level 99 players" have something to do with their money, build ghost towns!!! LOL