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It's possible.
The rocker and valve shim are held in place against the camshaft by the pressure from the valve spring. If the spring failed it's possible that the shim dropped out from under the rocker or that the rocker itself is misaligned. But that would hardly explain the low compression, at cranking speed, you're going to get a good cylinder fill from just one valve, that valve may not be seating well anymore. If you've still got the intake off, rotate the engine so no.3 is at compression TDC (all 4 valves closed), put some air in it and spray some soapy water on the closed valve.
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