With the latest beta, labels do not work for me.

With the following code:

\definelabel[Q]
\starttext
Label: \Q[abc]

Label: see \in[abc].

Reference: \reference[def]{2}

Reference: see \in[def].
\stoptext

I get:

and the log states:

references      > unknown reference '[][abc]'

while with tl18, I get the expected:

--
Rik