Well, some experts that gave their opinion to Business Insider (which is usually not an alarmist type periodical) that Putin is specifically sending a message.
Sergei Skripal attack: Putin 'wants everyone to know it's him' - Business Insider
In terms of the use of novichok, some reports I've read suggest that some of the compounds could be used in a binary way. That is, one part of the poison could be introduced to the victim without any negative effects, then it is just a matter of time and opportunity to introduce the second compound.
For instance, have someone ingest Part A with their tea on a Monday. Let's say it stays in their system for 3 days. Then, you'd have until Wednesday to introduce Part B.
That may also explain how the Skripals survived; the dosage was difficult to estimate.
Here is an article on the assassination of Kim Jong-nam. He was killed with a binary version of VX. https://www.theguardian.com/world/2017/feb/24/what-is-vx-nerve-agent-killed-kim-jong-nam-north-korea
In the case of the assassination attempt on the Russian spy and his daughter, 21 people were treated for exposure to the unidentified agent. If it was a novichok agent, the spy and his daughter are very lucky to still be alive. They will both likely suffer physiological exposure issues for the rest of their lives. https://en.wikipedia.org/wiki/Novichok_agent
The agents may cause lasting nerve damage, resulting in permanent disablement of victims, according to Russian scientists.[SUP][25][/SUP] Their effect on humans was demonstrated by the accidental exposure of Andrei Zheleznyakov, one of the scientists involved in their development, to the residue of an unspecified Novichok agent while working in a Moscow laboratory in May 1987. He was critically injured and took ten days to recover consciousness after the incident. He lost the ability to walk and was treated at a secret clinic in Leningrad for three months afterwards. The agent caused permanent harm, with effects that included "chronic weakness in his arms, a toxic hepatitis that gave rise to cirrhosis of the liver, epilepsy, spells of severe depression, and an inability to read or concentrate that left him totally disabled and unable to work." He never recovered and died in July 1992 after five years of deteriorating health.