Part of the problem lies with working on older aircraft, but there must be other data available somewhere. There is one very good reason for not seeing joint allowables for other fastener and sheet thicknesses. The strength of a joint is highly dependent on the fastening process, there are so many variables in process alone that very few of the parameters can be treated analytically. This will result in that process being changed and possibly all of the allowables becoming worthless. Signed SamX, former author of Boeing Design Manual sections on fastener allowables and joint allowables.
Life can be so non-linear.
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