While the Ducati factory never used F1A, F1B and F1S designations for the bikes, the USA importer Cagiva N.A. used them and they are printed on the parts fiches, advertisements and other paperwork that was distributed by the importer.

I have seen F1S VIN numbers ranging from 751806 to 751952, so from this we can conclude that at least 146 bikes were made (probably the 150 number is correct). All of the F1S bikes that I have seen had Kokusan ignition, so I don't know if they were considered a different batch than those F1b's that came to the USA with Kokusan ignition.

I have had both an F1B with Bosch ignition and original Motoplat coils and an F1b with Kokusan ignition, and the Kokusan bike started easier and ran better. The Kokusan ignition control units are a weak spot and are known to fail (especially the units with blue potting material), so I recommend always having a spare on hand. You can pick them up cheap on ebay, as they were used on all carbureted/air cooled Ducatis (Paso, 900ss, 600/750/900 Monsters) from the F1b until they went to fuel injection.