That may be true, but so far as the stats you are quoting are concerned it means that the private pilot certificate holders who obtained their IFR rating before becoming commercial or ‘higher’ certificate holders are ‘lost’ to the stats once they get that ‘higher’ certificate.
Tell me where in the stats it shows how many commercial or ‘higher’ certificate holders obtained their IFR rating as private pilots before becoming a commercial certificate holder. Your previous assertion as to the numbers assumes that no pilot who moved from being a private certificate holder to a ‘higher’ certificate holder in the US obtained an IFR rating before doing so. That’s a rather brave assumption.