Are tax reliefs not fully calculated in stock prices?

After months of delays and postpones, tax cuts are getting closer to reality. They, to a large extent, were at the base of the growth of US indices, leading them to new historical records.
But JPM, the US investment bank, has good news for the investors - the growth is not fully reflected in stock levels.
In a letter to investors on Monday, bank analysts said tax cuts were reflected in just 50 percent of stock levels. This gives space for the index to rise to 2,800 points by the first months of next year, according to analysts.

Trump: The tax reform will push the indexes up

President Trump said yesterday that his planned tax reform would make stock markets rise sharply.
The stock markets added $5.2 trillion of the November 8 election victory, or a 25% growth, according to Trump's post on the Twitter social network, where he is very active.
Trump added that unemployment in the US has been the lowest since 16 years. He said, that if the Congress has given an approval for the massive tax reliefs and reforms that he asked asking, the values ​​for the markets will continue to grow.
From November 8, the Dow Jones Industrial Average blue index rose by 25%. At the same time, the broad S&P 500 grew by about 20% and the Nasdaq by 27%.
In terms of unemployment, at 4.2%, it is the lowest since February 2001.
Trump did not hasitated to invoke the "fake media", to pay attention to the actual stock market growth figures since his election victory.
Market participants, however, are divided on whether the forthcoming tax reliefs are "reflected" in the prices of financial assets. Overall, they are unanimous that they will have a positive impact on the economy and stock prices in the medium term.