It is unclear how far the bore would have reached prior to the 1800s. Apparently cargo ships used the tide to carry them as far as Upton-upon-Severn*. Given the fords at Worcester, but the general navigability at this point, and the fact that the tide may reach there today, it seems likely the river was at least tidal there. Paintings prior to the 1840s (for example Bayliss* and Harral*) tend to show bankfull conditions so are little use. Camden* quotes Malmesbury's De gestis pontificum Anglorum of 1125 CE (biography) which notes the bore only reaches "the bridge", probably Gloucester (the earliest recorded bridge there is 1154 CE*, but earlier ones are likely). This would be less distance than now. It's possible the bore went further in the past. In its favour is the fact that bore waves require little water to maintain form*, and there would have been less obstacles. Against it is the fact that they need some water*, and the lower water level in the past would have left stretches of the river with little water and almost certainly rapids. While bores of an equivalent size can travel 100km inland*, the Trannon now starts many kilometers upstream, making it unlikely the bore reached it.