Can you place a meeple on a tile you didn't place?
You can only place it on the tile you just placed. From the Rio Grande edition rules:

After the player places a land tile, he may deploy one of his followers, using the following rules:

The player may only play 1 follower on a turn.

The player must take it from his supply.

The player may only deploy it to the tile he just placed.



While the Z-Man edition rules don't have a specifically spelled out restriction; you can go based off of what they do allow you to do:


Placing a meeple:
The player may place a meeple from her supply onto the tile she has just placed.


The sections on Highwaymen and Knights say something similar. While the rules don't say &quot;you cannot place a meeple on a different tile&quot;, they don't need to, because the rules are there to tell you what things are are allowed to do. You are automatically not allowed to do anything that the rulebook does not give you permission to do.
As an extreme example, the rules don't say that you aren't allowed to take one of your opponent's meeples off the board, but it is assumed that it is not allowed because they don't say you are allowed.
That being said, the Z-Man rulebook just doesn't seem as clear over all. It awkwardly states the rule for placing a tile multiple times; for each of the types of terrain, and then gives the rule about placing a meeple for each one. Under the rule for placing a meeple a a monk, it actually says &quot;You can place
a meeple on a monastery as a monk.&quot; which fails to mention that it must be on a monastery that you just placed. You need to use the context of how placing meeples in general works to realize that you can't just place a meeple on any monastery.