The Detroit Red Wings and the New York Rangers both claimed to hit the 20,000 goal mark in consecutive days, which sounded weird.
Turns out, there is a reason for that, as they both came to 20,000 goals differently.
The Red Wings only counted goals scored by players in regulation and overtime, bringing them to 20,002. If you do the same with the Rangers, it brings them with 19,921.
However, the Rangers have won 79 games in a shootout, giving them exactly 20,000. Applying this to Detroit, and Detroit has 20,072.

So, everything equal, the Rangers jumped the gun by adding shootout winners to the total.