upper left: 18420 series. Has welded skid bars in front. Some like the 18449 have the same upper loops but tubular skid bars bolted on
lower left, red one: 18420 series. Discharge chute has a distinct elevation from the rest of the deck. Jason told me the earlier decks had a tubular skid bar , later models used a simpler flat bar on top. So, the red one is an earlier model. The PM shows a front roller but not a front wheel. I think there were many variations within models.
upper right, lower right: 18423 series. The 18423 parts manual shows a front roller but my deck is tagged that model without a front roller. The PM also shows a level front bottom, but again mine has a variation - a raised front edge. Again, later models because the skid bar is flat on top. The rounded bar is stronger in bending but Bolens very slowly learned it was OK to build them strong enough and lessen cost, not build them like 1930's locomotives.
Many PMs show washout ports as standard. Useless, but standard. On the Backyard Round Table, one person said he found the most effective way to wash the deck was running the deck in a puddle deep enough to reach the blades. Like cutting water instead of grass. That really slings the water everywhere!