[coeff,score,latent,~,explained] = pca(X);
It is noted that there that coeff transforms the data from the original space to the PC space:
dataInPrincipalComponentSpace = X*coeff;
If we have data in the principal component space, we can transform back to the original space like this:
X_again = dataInPrincipalComponentSpace*inv(coeff);
That particular line of code will transform all of the original data points back from PC space to the original coordinates. Each row of dataInPrincipalComponentSpace is the coordinates of one of the original data points.
If you want to transform some other points, then just use those points' coordinates as rows. Here, I'll just choose those coordinates at random:
random_point_in_pc_space = rand(2,N);
random_point_in_orginal_space = random_point_in_pc_space * inv(coeff);
Instead of random points, you'll want to use the coordinates of your points (A, B, etc).
A wrinkle in your case is that your points are only specified by the first two PC dimensions, PC1 and PC2. So, your W could be
but it could also be
W = [17, 0, 2, -3, 5, -7];
In fact, an infinite number of points would project from your 6-dimensional space to your point W in PC coordinates, which means there are also an infinite number of data points from the original space that would transform to W.
I don't know your application, so I can't help you interpret the implications for you.