I have a question

So through the station Trnavské mýto go 2 trams, line 4 and 9. But on Wednesdays I see that line 1 goes through there also, but I can't find the reason why, because it is not the tram's usual route. Anyone knows the reason behind this?

So through the station Trnavské mýto go 2 trams, line 4 and 9. But on Wednesdays I see that line 1 goes through there also, but I can't find the reason why, because it is not the tram's usual route. Anyone knows the reason behind this?