Change rate of cross validation data, after training
Due to stochastic nature of NN training, the best epoch may vary upon each restart. In other words, at epoch 8, each of (the best, under-fitted, over-fitted) cases may happen. However, if you train multiple times and the best model is consistently found at (or around) 8th epoch, it is safe to say 8th epoch gives the best model away from under- or over-fitting, thus definitely validation set can be added to training set to improve the performance.

A more solid approach would be to plot the effect of training size (10% up to 90%) on the best epoch and the validation error. This means producing two plots (training size, the best epoch) and (training size, validation error), where each point is an average over multiple restarts. This way you can better find (1) the best epoch, and (2) the degree to which the added validation set will going to boost the performance on unseen test data, i.e. extrapolating the validation error for training size 100%. 

It is possible that performance goes flat after for example 70% of training set, implying that adding the validation set has no gain.