Yeah for POM's that aren't Sch 2 or 3, the drug or dose isn't a legal requirement at all surprisingly therefore all issues are either clinical/terms of service/other.
I've just had a look in the BNF and all the lithium carbonate preps appear to be modified release. As its not a legal issue then there's no requirement for it to be on the script. As long as its all clinically sound and there's no confusion on your part about what to dispense, theres no problem. I've seen a lot of scripts for "mesalazine 400mg e/c" tabs but what we give is Asacol M/R and as we know that a non M/R 400mg prep doesnt exist, there's no confusion.
For the MST, as the G.P. prescribed by brand, theres no need to put M/R. If it was written generically then he'd need to specify M/R so there was no confusion and to make sure you dont dispense the standard release morphine. You'd be able to tell if a doctors forgotten M/R on a generically writen script (from the dose being BD)