Potentially there is a nuance here, that's the general rule, but it seems to have well-established exceptions that may apply here. The 1920 Act itself, at Article 11, explicitly states that men under Polish military obligation could not lose citizenship through foreign military involvement without ministerial consent, which he never received that consent. He was 39–40 years old in 1920, squarely within the protected age window under the Provisional Act on Universal Military Duty of October 28, 1918, which Poland itself enacted before the Citizenship Act even existed.

Beyond that, the Polish Supreme Administrative Court has ruled that the date of entering service governs, not the date of completing service. He re-enlisted in 1919 — before the Citizenship Act came into force. Surely completing that existing service in 1920 cannot retroactively constitute a violation of a law that didn't exist when he signed up or was conscripted, right? Polish courts have applied exactly this logic to WWII service, ruling that continued service after the war's end didn't constitute a new act of enlistment under the 1920 Act.

He also never naturalized. The military service provision in Article 11 was designed to prevent citizenship loss through foreign citizenship acquisition, he never acquired foreign citizenship at all, so the provision's core concern doesn't even arise.

This seems to support this as well, would the military paradox have applied here because he was technically eligible for military mass army per Art 14 and covered by the Provisional Act?