They currently have the same 13 games. Six points with the remaining games of the season, there will still be plenty of opportunities.
Six points look big but it is small enough during a long season. 25 more matches will be enough for other clubs to catch Napoli.
The remaining 25 games will still be a World Cup. Napoli and Milan will probably still make a lot of mistakes. It's overconfident to say Napoli will definitely be champions this season. Remember besides that there is still a transfer market. If Milan or any other club has a lot of money I think Serie A will be even more interesting. Until now, they have never lost, they look convincing. Let's see until the end of the season.
At the moment, from the rankings, AC Milan are the most possible competitor with Napoli but it can change if Napololi lose 2 matches. Even Napoli have good form but losing two matches is not impossible. If they lose like that, it will give chances to other clubs under AC Milan to join the Scudetto competition.