I am not aware of any limit on the number of simultaneous MATLAB sessions you can have on the same host until a Named User license. Typically the limitation would be more the amount of memory required and the CPU time that they would use.
Floating licenses based upon login names do permit the same user to log in multiple times on the same host. There might be a limit on the number of times the same user ID could be used to log in on different hosts.
With regards to floating licenses dealing with number of simultaneous users: I do not know the current answer to whether one particular user would be considered to use up multiple slots if they logged in multiple times from the same host. Historically, the results were inconsistent, with it mostly being the case that only one license slot was used, but that from time to time I did observe it requiring multiple login slots.
