imho, vocab upgrade is normally done when the vocab is corrupted (no voice) for some reasons or if there are phrases in the new version that are not available in the older version. Furthermore, by upgrading vocab the existing recorded messages (e.g. greeting message, reminder message, or alarm message) are erased and need to be re-recorded.
Thus, I do not think you should.
The reason why the voice was lost and was recovered by a reset in this case is that Comfort detected a voltage drop below the critical level. The Voice memory was disabled in order to protect it. The voice is restored by a Reset
Hence the voice is missing, the first thing that should be done is a reset, which I forgot to mention in the earlier reply