Tom;
True, I have lathe cut threads with a sharp V tool. Note this will leave the sharp V Only in the root of the thread. When you get to the proper pitch diameter the crests will still have the flat. When you drill or bore the hole to the proper size for the internal thread those crests also will still have the flat. I have also lathe cut threads where it was a "Requirement" to put the proper flat on the tool for the part to met specs, just depends on it's designer & the use for which it is intended.
All the standard metric threads I am familiar with do have 60° V's. The Whitworths I am familiar with all had English pitches & 55° angles.
Mauser rifle barrels were fitted with a Whitworth thread having standard English pitch. Many have been rebarreled by US Gunsmiths with lathe cut threads having a standard 60° thread. They simply chased the thread until it would thread into the receiver & apparently no problems resulted from this practise.
