Yes, we improved the situation starting in 1991. That resulted in a significant decline in the number of people who declared several languages as their mother tongue. People were in a better position to understand that, in addition to asking them to state the languages they knew, we were trying to determine which one was the first language they had learned at home as a child. This did not prevent us from receiving multiple answers, but that number declined significantly.
On October 31st, 2017. See this statement in context.