Not sure about the
ServiceNow Add-On version 1.23.3 but you can find the Release history for the Splunk Add-on for ServiceNow of each version. Please check
Vendor products of the different version in below link.
@jacqu3sy oooh .... my bad.
I have also searched a lot in service docs but no luck. But I think, not sure, it should work for all the ServiceNow version which provide ServiceNow Security Operations application support.
Using the above link you can find the links tagged with almost all the supported version.