Is it possible to know what 都 means in "Subj + 都 + Predicate + 了"? In my lessons, I came across two different meanings for the adverb 都 dōu:

&quot;Already&quot; with the structure: Subj. + 都 + Predicate + 了, where 了 stands for completion of the predicate (see Expressing &quot;already&quot; with &quot;dou&quot; in resources.allsetlearning).
&quot;All&quot; or &quot;both&quot; with the structure: Subj. + 都 + Predicate (see The &quot;all&quot; adverb &quot;dou&quot; in resources.allsetlearning).

I wonder if it is possible in some sentences to distinguish between these meanings without more context. In particular, I'm thinking about the situation when the sentence has a final particle 了, such as:

她们都吃饭了。
1: They have already eaten.
2: All of them ate.

Maybe there is not much difference, but I believe in English there is a difference in the emphasis: in 1., the emphasis is on the time (they ate before expected); while in 2., the emphasis is on the number of people. For example, if this was a sentence said in a restaurant by a waiter on the phone, interpretation 1. could mean a particular table just finished eating then, while interpretation 2. could mean all tables finished eating.
It expresses "already" with the structure: Subj. + 都 + Predicate + 了


Only '了' indicates 'completion of a verb' in this structure

'都' in [Subj. + 都 + Predicate + 了]  mean 'even'.  Try write a sentence in this structure without 了, and you wouldn't say 都 expresses "already". 

Example:


"他(都)说 不知道" = "(even) he said he didn't know" 
"他(都)说 不知道 (了)" = "He (has already) said he didn't know" or "(Even) he said he didn't know"



  It is used for "all" or "both" with the structure: Subj. + 都 + [Verb Phrase]


The 'all' and 'both' meanings can only apply with multiple objects 

Example: 


[A and B (都) + Verb Phrase] = [A and B (both) + Verb Phrase]
[subjects (都) + Verb Phrase] = [subjects (All) + Verb Phrase]


For a singular subject, 都 cannot expresses the meaning of 'all' or 'both' . It can only expresses 'Even' or 'too/ also' (Cantonese)