I've decided to jump right in on my response this time since I've actually tried these two before. The addition of any pre-printed Sheep features on tiles definitely adds an element of desire to the game, something that can also be seen in Halflings I and The Shepherds. Unlike other sheep, the pre-printed ones don't disappear when the wolves come or when somebody scores. People can just keep scoring for these forever. Placing them on the River tiles, which are start tiles, seems to be a rather smart move since those tiles will be on the board for the longest, thereby maximising the potential that the pre-printed sheep will be scored repeatedly. However, the fields do run the high risk of being enclosed early, as often happens in my games with the River, at which point the Shepherd will have to "escape" in a fashion and the pre-printed sheep will be worthless from then on. Still, the benefits seem to outweigh the risks and I am always in favour of tiles in one expansion having features from another printed on them. The River seems to be a good and repeated choice in this regard (see also pre-printed Vineyards, Inns, and the Volcano).