Singer along with the Berlin-based agency "Culture Management Berlin" created a database of Singer sewing machine world productions in 2000 and 5 years later the list was finally finished and published in 2005.
This database is the first and only complete database of Singer sewing machines productions in the world.
A joint licensing agreement for offering this entire database on the Internet, print media is only between the Culture Management Berlin [Germany] and the Singer Corporation NV [USA]. The only production records from the Anderson factory is the "NA" Series Register Numbers in 1951 when a limited edition of only 10,000 Singer Model 301 sewing machines were allotted for Singer's 100th Anniversary.
That simply means that there were some Featherweights within that group of numbers, but it doesn't indicate with which number the group started or ended or how many 221 machines were involved.
For additional reference and a few more dates for those later year machines, however, we have included some of these dating records in the charts above, sourced from JJ & Leo's Featherweight 221 Factory site as well as uk's site.
The dates given below are the days on which those batches were started, together with the number of machines in each consignment.
The first Featherweights batched in 1933 begin with the two-letter prefix 'AD'.