Possible variant spellings of the name ...
HOLLDORF
Holdorf
Holdorff
Hil...
Hul...
...di..
...du..
Anything is possible;
  depending on what they were drinking and hearing in the early days.

According to the Social Security Death Records Index (SSDI),
     none of the family had the spelling Holdorf,
       but the majority had the spelling Holldorf; ALL of the tombstones
        in the family church cemetery have Holldorf.
The majority of the attendees at the 2008 reunion agree with the latter.