I do tend to ramble. This may be in part an attempt to cover too many side issues without delivering a five or six page analysis. Never the less, it does often get in the way of things...
Your questions, seem to be directed at my comments about experience, as it relates to remote measurements of lengths or distances, which I think are better described as judgements of remote lengths or distances, and the relationship between length contraction and proper lengths, with respect to measurements...
Experience,
I did not mean to say that experience is not based on past measurements, however judgements based on past experience cannot always be considered measurements.
We make judgements about measurements all of the time everyday, when we look across a room and judge an object to be 1 meter or 3 feet long or across. This is consistent with past experience and may be an accurate judgement, but it does not represent a measurement of the dimensions of the object.
We can make no remote measurements of distance or length that are not dependent on assumptions. The most fundamental of which is OWLS. {Going any further into this here would be rambling again and the issue could be a subject of its own.}
Length Contraction and proper lengths,
Length contraction can be confirmed by similar remote judgements about the lengths of moving objects. That is objects moving relative to the point where the judgement is being made. (Again I am using the word judgement here because we cannot use a ruler from one frame to make direct measurements in another frame.)
The problem with experimentally confirming length contraction is that unlike clocks, rulers do not retain any persistent information about any length contraction, they may have undergone while in relative motion. (This assumes that we have some means of identifying that an object has been in motion with respect to some other frame.)...
How this relates to proper lengths is similarly experimentally unprovable. Once again, say you know that an object has experienced acceleration and thus some length contraction relative to a starting and ending frame of reference, any measurements of proper length, which would have been length contracted, have no persistent character. Proper length is always measured from an object's rest frame and thus never differs as an object's velocity changes... And an object's proper length cannot be directly measured from a remote frame of reference.
In almost all cases, within the context of SR these comparrisons involve the use of Lorentz transformations, which are not measurements.
P.S. I often add the "current technology" disclaimer, because even in my own life time I have seen such improvements, that I don't want to suggest that the technology will never exist to experimentally test and prove, many of the theoretical issues discussed.
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As far as I can tell, there has only been one valid argument against the idea that RoS is measurable. That argument is as follows: "Measuring RoS depends on Einstein's definition of simultaneity, which is not something that is measurable."
