Cisco AAA/Identity/Nac :: ACS-1120 Large Deployment License?

i  have 4 X ACS-1120. Each 2 are operating as an Primary and backup. I  want to add a license in order for the ACS to support more than 500  networks which includes in the base license.As I understand this is the license required : L-CSACS-5-LRG-LIC=
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Is this license applicable to ACS-1120 appliance with ver 5.2 ? – I understand that it is. for my scenario, do I need to purchase total of 2 X L-CSACS-5-LRG-LIC=  (one for each environment, one license will serve 2 X ACS in Primary  and Backup) or I need to purchase 4 licenses each for each ACS ? – I  understand that one license will serve deployment of two ACS in primary  and active scenario.