What would be useful now at this stage in the discussion would be a restatement of ALL the available published official or semi-official statistics on Eastern Front casualties: Russia / Soviet Union; Austria-Hungary; Germany; Bulgaria; Rumania; Serbia; Turkey; Lithuania; Latvia; Estonia; Poland; Hungary; Czechoslovakia to cross-check the variances, discrepancies and overall reliabilities of such officially reported stats.
Recommendations:
1) That as many of the better(best?) current historians from each of the above states be contacted and requested to furnish with documented sources what they believe casualties on the Eastern Front to have been in what was or became in whole or in part their country/state for any belligerent engaged. This should be a matter of time and logistics using the internet and various discussion groups including history groups that surely most if not all of these countries have.
2) That as part of this process that ALL officially published histories including official military medical histories be reviewed and their "historic findings" presented in a clear concise and systematic fashion here on GWF broken down by state/country; belligerent force; date(s); theaters of operation/fronts...
3) That hitherto unknown, or hardly used especially primary sources on casualty reporting be ascertained through a diligent search through all types of archival depositories and not just central state military archives, to publicize future research into casualty research for the Eastern Front of WWI overall. I am thinking of such archives as:
a) Red Cross Society (National) archives; [ despite fairly intense closure normally to such national archives see

infra for a clear impulsion to have WWI era archives "opened" ]

International Committee of the Red Cross Archives which is in the process of making their POW card catalogues available;
c) Provincial / Regional archives such as the Russian "gubernia" archives for casualty reporting related records through direct or indirect regional/local authority connections and interventions for casualties such as burial, cemetery, missing persons reports, judicial / legal....
d) Neutral observers and/or visitors such as journalists; medical personnel and missions - information given to them at the time, direct observations/comments, photographic documentation....
e) Central state but especially regional, provincial, local/municipal/ rurally based war charity records such as the ZEMSTVO records for Russia / Ukraine / Poland.... Local hospitals, local war charities such as wounded soldier comforts committees - ledgers, accounts, reports, histories, audits, correspondence....
f) Provincial, local, regional newspapers: while war time censorship undoubtedly played a very heavy hand throughout not least of which are Russian papers - some information might be gleaned for particular engagements, specific hospital death rates/figures, cemeterial/burial reports, and the like.
g) Central and/or provincial/regional death records - burial records - cemetery records.
h) National, provincial, local current day genealogical groups in these former Eastern Front countries might be enlisted to study particular areas/locales, cemeteries, military burial sites, ethnic groupings, occupations, etc....
i) Current day both professional and amateur battlefield and war related archaeological investigations and reports/documentations. Usually too specific or materially culturally oriented they can still be useful for geographically based information related to casualties, newly found burials/sites, etc....
Now if one had unlimited money, limitless time, spoke all the primary languages of these countries (at least a baker's dozen!) this would be easy!
John
Toronto
Canada