As a data point, my Regina freewheels are newer CX/CX-S 6/7 speed and the 7sp is like the lefthand one--flush in back with the low cog extending past the lock ring. 6SP is flush in front, being 5mm narrower. I'm inferring the one on the right is earlier, being a complete departure from newer models.

As to what's with the lock ring in back...is that the only way to get at the bearings?