Many of us use Reach and Frequency, are we following it blindly? Is it still relevant?

Does anyone know the statistical formula (calculation) for reach and frequency? Not the individual definitions of Reach and Frequency or the formula R X F=GRP - but how reach is really calculated from GRP’s, and how the frequency curve is derived? I Googled no real results.

When was the Reach and Frequency formula invented or last changed? I know Nielsen started measuring TV in 1950, is that when the formula was invented? There were 3 networks back then.

Does anyone know the margin of error on reach and frequency? I Googled it and can't find it. I Googled Nielsen margin of error and I can't find that either. I do know the margin of error is high on individual ratings and it increases as ratings get smaller. Based on media fractionalization it must be increasing. Is the margin of error from a single rating multiplied when it is calculated into the reach and frequency formula?

I worked in Broadcast TV for 32 years. I never believed the reach and frequency calculation. as broadcast moves to digital Local CTV | OTT advertising there are better measurements for Reach and Frequency, targetability, and control of messaging.

Is traditional reach and frequency still relevant. With CTV | OTT there is better measurement, targeting, control of messaging