Honestly, those small bits from the future always get me curious. From how much work is put into hiding Tanya's name or every hint that might lead to her, was it the work of the gods? Since he/she won't go back to the cycle of death and rebirth. But then it wouldn't make much sense for her not to be erased from memory as well, so perhaps it was "divine inspiration" or some subtle influence that led to the work being done by humans. Or maybe Tanya survived the war and either defected to another country/power to start anew and the sinking ship (empire) did all within their power to protect/hide her war crimes/contributions so that she wouldn't be persecuted or targeted for it. The way it keeps happening in documents, photos and any kind of register, despite currently her mana signature and appearance being already identified by both allies and enemies - which means there should be someone who could reveal it. Other possibility is that they all got into agreement that a child playing a role during wartime it was something terrible that should die with the end of the war or so out of touch with reality that it must be a collective hallucination born out of madness and the battlefront gossips.