The immediate problem with the method of developing your formula that is described is that it assumed that the pay of your staff before you had a systematic formula already accurately reflected prevailing market wages in the locality of every employee.
And, for US locations, BLS data is readily available publicly. While that may not have been a suitable source for a worldwide formula, it would have at least been a suitable reality check on the validity of the formula you came up with to see if it reasonably approximated the variations in market rates within the US.
And, for US locations, BLS data is readily available publicly. While that may not have been a suitable source for a worldwide formula, it would have at least been a suitable reality check on the validity of the formula you came up with to see if it reasonably approximated the variations in market rates within the US.