From: https://github.com/abisee/pointer-generator/blob/master/beam_search.py#L111

In decoding words, we change the token id to the unkown id if t<vocab.size(). So if the decoder is pointing to that particular token it produces [UNK] in output. Is it correct? Following the paper it seems that the decoder should be able to point to that token and copy it, instead of copying the unknown token. I think it's the whole purpose of the pointer-generator model to handle oovs. But from some experiments in decoding I see that the models often outputs some unknown tokens.
I tried replacing the 50k vocabulary to the full vocabolary but I get cuda device asserted errors.