Hello.
I have major problems with the recognition of Voice Commands.
I observe that the incorporation to the Vocabulary of some phrase, that phrase becomes preferred over others with similar phonetics.
For example, if a voice command says “Volume + 2”, the recognition of “Volume - 2” would be in difficulties, which has led me to also add “Volume -2” to the Vocabulary, and so on with a multitude of situations.
The result is a vocabulary with a number of elements that becomes disproportionate in size and, worse still, with an increase in the number of errors in interpretation, which makes the operation disastrous. 
To try to improve the situation I have deleted a large number of elements from the vocabulary and the situation has worsened.
It seems the appearance of the utility “Vocabulary” instead of a help has become a traitor.
My question is if there is any known cause that justifies this situation whose repair will solve these errors in the recognition of Voice Commands.
I appreciate any help.
Greetings