Quoted from frenchmarky:

My Black Knight has one connected to those traces, so maybe yours is an older board before the cap was added to the circuit and somebody else added it. (?)
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Quoted from barakandl:

It is normal. Boards found in Gorgar usually look like this. WMS must have realized they needed more bypass capacitors. I think there is one more bodged soldered right onto traces like that.
Also beware that one electrolytic cap is marked with the wrong polarity on that first version. It is 1uF near the amp. Some of these very early sound boards are found with a white silk screen layer WMS was never using in that era which is kind of interesting. Yours does not...

Quoted from barakandl:

the picture on pinwiki even has this cap installed "backwards". With a DC blocker does polarity matter? Voltage will be low. Seems like WMS rectangle shaped board had the cap the other way.
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Quoted from barakandl:

sorry, i went a bit off topic. just pointing out C12 polarity marker on the PCB top copper layer of your board is wrong per the schematic and how the board originally stuffed by williams factory, but not matter much since the rectangle version had that cap in the other way.
I can see an original C12 in one of your pictures. The original part's polarity looks correct per the schematic and the updated version PCB marking, so I would put the replacement in with that same polarity, the positive leg on going to the amplifier pin.