I agree David , we can only work on what is there but we shouldn’t ignore taphonomy , degradation , secondary use etc .In the case of a recumbent stone circle with only one flanker it is reasonable to work from the supposition there may have originally been two . Also it hasn’t stopped astroarchaeologists suggesting orientations at sites that no longer have anything visible for sightlines e.g. Woodhenge .
Dating any monument from it’s putative astronomical alignments should not be a consideration particularly when we have no idea of the level of accuracy or even whether the monument was intended for such a use , not that it would make much difference in this case if the suggested orientations are solar .
I aware of Lockyer’s mentions of the Hurlers etc in SOABSMAC but not Trevethy , could you point me to the ref please ?
Have you looked for the same patterns at other local quoits ?
George
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