WW1 GGF who was uusr hadifogoly

Ok , GGF born in 189x in modern territory of Hungary, then hadifogoly in 1919 by soviets, then died in 197x in ussr.

Are there any reasons to hire lawyers even to go through the citizen verification. Docs listed above exists . Family Tree looks like : ggf - gf - mother - I.

The problem is GGF, no children or wife certificates from HU..

Are there any real examples you went through, as long as gov.hu docs shows , you need to prove , he has not lost citizenship w/ links to 1929.. I read it all , and think about lawyers now. Any private experience, please dm me if it's not for publicity.