When an issue is deleted, associated OS_CURRENTSTEP and OS_HISTORYSTEP records are not deleted. This can be shown with the query:

select OS_CURRENTSTEP.ID
from OS_CURRENTSTEP left join jiraissue
on OS_CURRENTSTEP.ENTRY_ID=jiraissue.WORKFLOW_ID
where jiraissue.WORKFLOW_ID is null;

And _PREV step tables.