What is recognized most reliably will depend on your specific configuration (including your microphone, how you speak, your environment, etc...)
Extremely short inputs like that offer very little information for the speech recognition system to work with, making accurate recognition more difficult.
That said, on my machine they are recognized fairly consistently (as you'd expect given that numbers are a commonly used input for just about any speech recognition system)
Have you completed the speech recognition training at least three times?
If you find that a specific word or phrase isn't recognized accurately despite extensive general training, you could try adding it the the dictionary with a custom pronunciation: Click the wrench icon on VoiceAttack's main window, and on the "Recognition" tab of the VoiceAttack options window click the "Utilities >" button, then choose "Add/Remove Dictionary Words"
Adding "alternate" words can also be an option, though I personally wouldn't consider it the first thing to try, perhaps unless you're distributing your profile to other users who report similar recognition inconsistencies.