why didn't the Vulcan crews have their charts?
It would be interesting to know how many charts had already been grabbed by the RN before they sailed... I would guess that the entire stock had gone afloat or was at Northwood.
In any case.... a map is not accurate - a chart is, and just having the plotting squares was more than enough for the Nav Plotter to get down to the region. I wonder how many baby Navs at Finningley had to glue an extension onto their plotting chart of the South West route and manually add a few extra grid squares? It was quite common with manual air plot and a strong jetstream!