How old is the Machinery Handbook? AWS A2.4 was updated last in 1998. The biggest change I found in the welding symbols at that time was a change in the flange/edge welding symbol. There are some more text changes but nothing too big. If the weld symbol(s) in question is not the edge weld symbol, you can probably go with what you have. If you will e-mail me I will e-mail you a scanned copy of the chart in the back of the current AWS A2.4-98. Hope that helps.
Depending upon the year, there may be differences in the field weld symbol. The flag vs the filled circle at the arrow line, reference line junction.
This is what I speak of http://www.weldinginspectionsvcs.com/weldallround.htm .
I would think the machinery handbook would indicate where the symbols are t aken from. I am highlyconfident they were not generated from "scratch" but may have been taken from an older A2.4.
Havea nice day
Gerald Austin