If you look at the code, they seem to follow a similar convention. But the computed GOTO described above is using a set of labels employed for what looks like an inner state machine, related to a previous inner state machine (thus the offset by 20). It seems perfectly reasonable (preferable, even) to use an entirely different domain of numeric labels, distinguished by length, for those parts of the code.
the convention I used was taught was always 4 digits always increasing going down the pages.
7000 and 8000 range where for input and output FORMAT statements, 6000 was used to label code 6999 was always the exit