Take a look at http://www.cisco.com/en/US/partner/prod/collateral/voicesw/ps6788/vcallcon/ps7293/reference_guide_c07-566560.html#wp9000408
Reading through this I understand as bundled are 20 SSL VPN users. Only way to increase is to buy 8u license increases for UC500 platform.
This conflicts with data sheet for sku you list. This shows uc500 in one instance, but for part number description does not list uc500.
I would run this question by Cisco licensing team because of conflicting information.
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