So I have an interesting spoon, it looks to have incomplete hallmarks, it has a maker's mark(?) of JG, a Thistle and a Duty Mark, but lacks a date letter or a city mark. Any ideas on why its missing those 2 features?
This looks like an Edinburgh mark missing, as you point out, the castle town mark and date letter. Hallmarks with missing components were not unusual at the period this was hallmarked; we can date it approximately by the form of the duty mark and sterling mark to between 1797 and 1805. JG is not known to me although there are several candidates who were working at the time including several called John Graham variously working in Glasgow and Edinburgh.