Bonnie,
One way might be to make a take a copy of the old RACF database (with the access still there) and check the sim_via_group. Or use RACF-Offline to create such a database and use it as input along with the historical access event records.
The UI has some options in AM.1 -> Simulated fields selection -> Essential group Y/N etc. that might also help.
Regards, Mike
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