I agree with Eddy, Could have slipped, I don't like that fitting, I always stuff a rag inside the tapper, With a screw driver, To try to clean the oil out, Just before fitting.
As I said before, You can check by eye, Looking down the plug hole, To see the piston just before TDC fully retarded, Just check it's on the right cylinder, Then turn the engine over and check on the other cylinder.
Just to make sure you are on the right cylinder, Take all 4 of the valve caps off, And the cylinder you are checking at TDC, Both the pushrods should be able to turn with your fingers, ie Compression stroke.
The trouble with not doing it for another year, It might not as good as now, The petrol will have gone off a bit,
And some oil may seep down and what we call wet sump, A lot of our bikes do it over Winter.
That can make it hard to start, Has anybody told you about that, Might be worth checking now ?.
Good Luck, Bill.