Ukranian casualities are classified by the goverment, as well as the location of mobilized solder during his first 90 days of duty. That's gives an possibility to the govement say literally any numbers of casualities.

There are indirect pointers of heavy casualities: introduced military duty on women, introduced mobilisation of infected with tuberculosis (non-officially), hard to leave the country by men, catch civilian attempts to mobilize on streets etc.