The questions wording (discrete, valve) makes it sound as if it's about early systems, not microcomputer and maybe not even mini-computers.
Here it may be safe to distinguish one off machines (which covers moste valve based) and in numbers produced units. One-offs were usually also full or in part developed by their users, so circuit diagrams were of course inherent parts of them.
Manufactured machines in contrast did (usually) not have such supplied to its users for their direct use, but they were more often than not part of the maintenance set stored at the customers site. Depending on manufacturer, model and installation, this could be several cabinets/shelfs of repair parts, tools (including oscilloscopes), consuambles and sometimes literally hundrets of folders with machine documentation, not part of user manuals. This was done so maintenance/service engineers don't had to carry a carload full of paper for each job.
This was done pretty consistent up into the mid to late 1980s ... or about the time when boards became less (on site) repairable and, more relevant, it became less possible to trace errors down to single components due the fact that integration simply took away most possible points to check while looking for a cause.
During later years (mid 70s) more and more documentation got moved into microfilm to save space, wo a micro-fiche reader became as well part of the (customer stored) maintenance setup for a mainframe.
And no, all of this was not given to customers in any way. They were proprietary documents for sole use by (manufacturer employed) service personal.
Of course, this may (and was) different handled for mini computers, system that often were configured / extended by customer side personal. Here it was about board documentation and alike, including schematics, at least for interfaces, while over all documentation was to be done by whoever configured a certain setup.