SAL (subscriber access licenses) can be complex and without question the number one underreported licenses under SPLA. Why all the confusion stems from misinterpretation of the SPUR and/or bad advice.
When you report by user, you have to take in account each user that HAS access to the software, not who does. Microsoft is not based on concurrent licensing. I wrote about this prior, but thought it was worth repeating. If you have 5 users that use the software, but 15 users can access at any given time, you must report all 15. Seems ridiculous, but is 100% true. Consider licensing by processor if user licenses become too difficult to track.
Read this section of the SPUR (use rights). “You must acquire and assign a SAL to each user that is authorized to access your instances of the server software directly or indirectly, regardless of actual access of the server software.” It’s the last part of that sentence that can get you in trouble “regardless of actual access of the server software” For a copy of the SPUR check out http://spur.microsoft.com/products.aspx
Thanks,
SPLA Man
SPLA Licensing 
Shelly
November 28, 2013 at 9:55 pm
Are there any tools avilable or scripts than can give to user count with access to a server?
splaman
November 30, 2013 at 9:07 am
Not that I am aware of. There used to be a company called Active Aeon (sp) who had an auditing tool specific for SPLA. I believe they are no longer in operation. Make it part of your contract with your customer that all users have to be reported, regardless of actual access.
Sam
September 13, 2016 at 8:02 am
Have the rules on Concurrent usage changed?
The July 2016 SPUR, under the Subscriber Access Licenses (SALs) for Desktop Applications section says,
‘Concurrent Connections for User SALs
Customer must acquire a SAL for each concurrent connection to a Server running the software (including by the same user from multiple devices).’
I am having difficulty working out how this applies to Office running on Remote Desktop Server…
splaman
September 15, 2016 at 4:38 pm
All that means is you can access from any device, just not multiple devices at the same time.
Daniel
July 30, 2019 at 3:28 pm
Sorry to reply to an old thread but I cant find my answer.
Does a user need a SAL for RDS and Office (reported separately), or does one SAL (installed in RDS Licensing) cover all SAL related software on that server for that one user?
MS Licensing
August 5, 2019 at 5:00 pm
They would need a SAL for Office and RDS