Once again very observant a trait I really like in people, I hope many are looking in as we talk about this item of interest.
Being a 3 bay barn this is the #3 bay and is the section that hay is stored in, meaning that the hayloft decends to ground level. This would indicate then that the irregular variation of the top of the sill creates no problem,
Now as you move to the centre bay that did have a floor covering of 3", pine slip tongue planks this irregularity could cause you some distress.
Remember now that this sizing had to be done at each vertical post at its point of contact with the plate, to ensure that the whole frame would go together properly, no mistake about that. To overcome this slight iregularity you would just get out your adze and in about 30 minutes or less cut away the proud material.
That is exactly the way that these types of problems as they arose were handled.
It could be that in the centre bay section very little needed to be taken at the sizing points so there may not have been a problem at all.
This is what using rough hewn material is all about, you expect these types of problems from time to time, and you handle them.
By the way I would say that a level eve is visually quite important
I hope this answers your question and I thank you for it I hope everyone enjoyed us sharing this bit of historic timberframing information
