You are absolutely right. The arrow labelled 'G-18' has a corresponding label to G-6, which also says 'TO #14'.
I am pretty sure that 'TO #xx' is the name of a unique label 'TO number xx'? 'TO' might be an anagram? I cannot see any significance to the number other than it is unique on the schematic, i.e. it's not a sequence starting at 1.
OK, here is another symbol that is puzzling me. A Circle with a Switch inside refers to the drum (Motor) unit. The number on the right designates the sequence 1, 2, 3, INDex and 4. The letter designates the switch location as Outside, Centre or Inside. However, one symbol has 'IMPulse' as the sequence and '5' as the switch location... what does this mean?
Clarification: the schematic I am working with is for Williams Kick-Off 1957 but I have the slightly later European version called Soccer Kick-Off. I assume the machines are identical other than the minor changes to the Back-Glass?