"you can only use RS-232 at a length of 50 meters max"

The "RS232" spec specifically states (in section 3.2) that, "The maximum length of the cable is not defined; it is determined bt yhe electrical requirement in 2.1.4 (see Annex A for guidance)"

Basically, what that means is that you can use cheap cable for short distances or expensive cable for long distance: it is the characteristics ("quality") of the cable that determines the maximum transmission distance - there is no arbitrary maximum distance stated anywhere in the spec!