start_ts_after_internal_nas: Start a Time Series after the Last Internal NA
Description
Internal NAs can cause trouble for time series operations such as
X-13-ARIMA SEATS seasonal adjustment. Often, internal NAs only occur at
at the beginning of a time series. Thus an easy solution to the problem
is to discard the initial part of the data which contains the NA values.
This way only a small part of the information is lost as opposed to
not being able to seasonally adjust an entire series.