W ' s ▁often ▁il leg ible ▁hand writing , ▁and ▁made ▁various ▁suggestions ▁for ▁improvement , ▁most ▁of ▁which ▁were ▁accepted . ▁They ▁worked ▁together ▁on ▁sym phon ies ▁nos . ▁ 6 – 9 , ▁the ▁opera ▁The ▁Pil gr im ' s ▁Progress , ▁the ▁T uba ▁Con cer to ▁and ▁other ▁works . ▁ ▁In ▁this ▁way ▁he ▁was ▁able ▁to ▁produce ▁manuscript s ▁that ▁were ▁even ▁more ▁author itative ▁than ▁the ▁composer ' s ▁original s , ▁since ▁all ▁issues ▁of ▁notation ▁had ▁been ▁discussed ▁and ▁clar ified ▁with ▁the ▁composer ▁himself . ▁He ▁has ▁been ▁described ▁as ▁" the ▁most ▁important ▁surv iving ▁witness ▁of ▁V aug han ▁Williams ' s ▁technique ▁as ▁a ▁music ian ". ▁ ▁Douglas ▁was ▁not ▁generally ▁exposed ▁to ▁R V W ' s ▁new ▁compos itions ▁until ▁they ▁had ▁been ▁substantial ly ▁sketch ed ▁in ▁short ▁score . ▁For ▁example , ▁he ▁was ▁first ▁made ▁aware ▁that ▁R V W ▁had ▁written ▁his ▁ 6 th   Sym phony ▁in ▁a ▁letter ▁from ▁the ▁composer ▁dated ▁ 1 3 ▁February ▁ 1 9 4 7 , ▁but ▁he ▁was ▁not ▁given ▁the ▁score ▁to ▁work ▁on ▁until ▁almost ▁seven ▁months ▁later . ▁ ▁In ▁an ▁apparent ▁departure ▁from ▁the ▁usual ▁method , ▁Douglas ▁was ▁asked ▁to ▁write ▁out ▁the ▁score ▁for ▁the ▁T uba ▁Con cer to ▁in ▁ 1 2 ▁days ▁to ▁meet ▁a ▁dead line , ▁but ▁without ▁the ▁opportunity ▁of ▁checking ▁with ▁R V W ' s ▁piano