This allows us to resume a harvester that was stopped due to dead time when the file is updated again. In our case it was a log rotated and remained empty for a weekend (system used only during week) and logrotate.d was set to not rotate empty files.

Come Monday file changed - so this allows us to pick it up again where the last harvester left.

The registrar data is only intended to be read during startup as the "last known fully acknowledged position that can not otherwise be known accurately during startup" (that's my view tho). With this case we need to resume after even unacknowledged events that may still be stuck in the publisher pipeline - for example server side crashed Saturday and someone figures it's fine to wait till Monday.

It is also easier to make the one way link from Prospector to Harvester two-way than to feed information back from Registrar that sits at the other end of the pipeline.