And yet :

IR 17

1737-1769: Cajetan Graf Kolowrat-Krakowsky

1769-1773: no Inhaber

1773-1780: Johann Baron Koch

1781-1796: no Inhaber

Source: Andreas Graf Thürheim

Gedenkblätter aus der kriegsgeschichte der K.K. oesterreichischen armee

Volume I

http://books.google.com/books?id=omBIdldTKUkC&printsec=frontcover&dq=editions:0jsjPd9UGXm8d#v=onepage&q=&f=false

Volume II

http://books.google.com/books?id=qcADAAAAMAAJ&printsec=frontcover&dq=editions:0jsjPd9UGXm8d#v=onepage&q=&f=false

These works do not however list Prince Ferdinand as an Austrian Field Marshal nor an Inhaber of an Austrian Regiment.

Good hunting.

Ron