Technically they aren’t numbered, they have a label. Labels serve as jump targets, have to appear in columns 1-5, must be numeric and all different, and should appear in order, but I don’t think they must.

(If they must, https://en.wikipedia.org/wiki/Fortran#Simple_FORTRAN_II_prog... is in error. It has label 601 follow label 799)

Of note is the statement

    if(m-n1)32,33,37

That jumps to label 32 if (m-n1) is less than zero, to label 33 if it is zero, and to label 37 if it is larger than zero.

Because those lines are jumped to.

I might be showing my age, but we used to number the lines manually, but then we would leave gaps in case we needed to add lines in between.

I think the numbered lines are branch destinations, but I can't find a goto 29 in there.