The age given at death would point to 1745 as estimated year of birth. But if he was hijacked around age 18, this would rather point to a birth year between 1759 and 1763.
The military sources give his place of origin as Watzendorf. There are two places with this name in Germany, but only the one near Neuendettelsau makes sense in this context, as the other one is far from any Rührschneck sighting. This Watzendorf near Neuendettelsau as well as several places with the name Waizendorf were checked, but Jacob could not be found in those places.
He could finally be found in a place a little west of the Rührschneck center. Lacking any other Jacob in all the places examined so far, there is little doubt that the identification is correct here.
"Watzendorf" may finally turn out to be not a place, but a district, the Amt or Vogtamt Waizendorf. Clues in this context will be checked further.

No death entry found for him or for any other Rührschneck in Aufkirchen 1750-1756.
The Aufkirchen christening records of the time around 1750 usually seem to bear crosses as notes when someone died early. There is no such cross for Johann Jacob, which implies that he survived childhood.

Entered military service at Nijmegen, Netherlands. No. 84 on the list. Company no. 10, under Friedrich Ludwig (Albrecht) v. Eyb, Bayreuth.
Left the army in June 1783, probably deserted. Appears as Johann Rührschneck in the list.

• Married: 25 FEB 1784 in Shenandoah Co., VA ²
• Change Date: 31 JAN 2008

1. John RASNICK b: ABT 1786 in Russell Co., VA
2. Jacob RASNICK b: ABT 1788 in Shenandoah Co., VA
3. Elijah RASNICK b: 1788 in Shenandoah Co., VA
4. Margaret RASNICK b: ABT 1791 in Russell Co., VA
5. Lazarus D. RASNICK b: 23 MAY 1793 in Russell Co., VA
6. Christine RASNICK b: ABT 1796
7. Nancy RASNICK b: ABT 1798 in Russell Co., VA
8. Mary Polly RASNICK b: 1800 in Russell Co., VA
9. Jonas RASNICK b: 13 AUG 1802 in Russell Co., VA

1. Title: Christening entry for Johann Jacob, son of Johann Georg Rierschneck
   Abbrev: Aufkirchen, lutherisch, Taufbuch, 1752.12.17
   Text: Anno 1752 getauffte
   41
   Irsingen
   Johann Jacob ward den 17ten Xbris nachts um 12 uhr gebohren und wegen groser schwacheit von der hebamme Poltererin in beyseyn deß vatters und Barbarä Deublerin gleich geh getaufft, der v. ist Johann Georg Rierschneck ein bauren-knecht daselbsten, die m. Anna. G. war Johann Jacob Vogt, hfst. Brdb. Onltzb. söldner und m. schuhmacher zu Schobdach.
   Repository:
   Name: Regensburg LKA
   Date: 31 JAN 2008
   
   Date: 8 AUG 2007
2. Title: Fetzer M.
   Date: 31 JAN 2008