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Drop frame doesn't work too badly on short programmes, as all editing software has been designed to cope with its peculiarities. Generating it in the long term requires all sorts of corrections as there is no simple relationship between clock time and dropframe TC.
It's all due to a decision made at the start of NTSC colour, long before TC was invented. The relationship beween colour SC and sound carrier had to be set to minimise certain crossmodulation problems. It was felt that moving the sound carrier by 0.1% would upset too many existing receivers so they moved H, V and SC frequencies instead. We've been living with the consequences ever since TC was invented.
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