It's understood when assembled (8)
I believe the answer is:
gathered
I believe this clue is a double definition.
'it's understood' is the first definition.
('gather' can be a synonym of 'understand')
'assembled' is the second definition.
('gather' can be a synonym of 'assemble')
'when' acts as a link.
(Other definitions for gathered that I've seen before include "Collected - inferred" , "Understood" , "Drew" , "Gleaned" , "Collected in one place and concluded" .)