إِنَّ الْعَمَلَ مُتَقَنٌ. إِنَّهُ مُحْكَمٌ.
The work has certainly been done well. It is indeed firmly executed.
Where the second clause substantially reinforces the first assertion, there is a case for complete connection through emphasis. By contrast, in 'The work was delayed. The rain grew intense', the second statement gives a reason rather than restating the first judgment.
Both examples may employ faṣl, yet for different reasons. The absence of wāw alone does not establish istiʾnāf; the analyst must distinguish reinforcement of an assertion from supplying an answer invited by that assertion.