I have db with data. Added _AUD tables. Data is not yet modified therefore _AUD tables are empty. I need to get revision by current date. It is initial revision from data tables not _AUD tables. Is there a possibility to fill _AUD tables with initial revisions for all data or get initial revision in other way? It is possible to look for initial revision in data if there is no data in AUD table for entity with id. But if there is data in _AUD table then initial state is not saved at all. I think it is a common case to deal with for auditing, that is why i'm asking a question about how to do that.
Not automatically. You should create a revision "1" manually (just insert into REVINFO), and then for all existing data add entries to _AUD tables with that revision.