Prior to the introduction of the SLA Engine (in the "Fall 2010" release), SLAs were processed by the “Escalation” engine that allowed each Task record to be associated with a single SLA. The fields “SLA Due,” “Made SLA,” and "Escalation" were maintained by the Escalation engine. This legacy SLA engine is still the only one used in Express instances.
The modern SLA engine improves on the original by allowing multiple SLAs to be tracked against each Task record. Users can understand if a particular Task SLA record has breached by viewing the individual Task SLA records - for the 2010 engine the Stage field will show Breached and in the 2011 engine a new "Has breached" field is used.
The Escalation engine is still present and running in the system as it also supports Inactivity Monitors (For more information on Inactivity Monitors, pls see product documentation topic 't_SetAnInactivityMonitor'.), even if you are using the SLA plugins, and this server-side code might change the value of the made_sla field when the task is closed.
If there are existing task records in the system that have the legacy SLA fields populated, they could be old records created in earlier releases. However, this does not impact the modern SLA engine in any way. The legacy fields can be ignored. Further, because the values may change unexpectedly, they are not intended for customer use.
If you still see new task records being created with values populated for these legacy fields, then you can check if they are intended to be used by verifying the System Property "com.snc.sla.run_old_sla_engine" to check if your instance is still configured to use the legacy Escalation engine for Service Level Agreements. If the property is false, you know the fields are reserved (because they are manipulated by the system) but the contents are not relevant. You can also check the contents of the legacy Service Level Agreements definition table ("sysrule_escalate"). Be aware that depending on how you access this table you might see both legacy SLA definitions and Inactivity Monitor definitions.