You need to get past the initial sandbox (5 posts or 5 days of membership, whichever comes last) in order for the ability to create new tags. First time posters can't tag their article with My-company-name. It's always been that way.
But, as a simple textbox, it was frustrating for newbies, because they had no idea what tags existed already or what they could use, so everytime they started a thread and entered tags, they'd get an error message saying they couldn't use the tags. And they didn't have a clear grasp of why.
No problem. Tags were optional. So I just disabled the tags field for newbie posters, and life went on for the past year or so like that.
However, since tagging is no longer optional, I felt that we needed a better way to make it easy for newbies to understand our tagging system. So what I do for newbies is, instead of presenting them with an autocomplete textbox, I first make them choose the forum they want to post in, and then I present them with a list of the 20 most popular tags in that forum. Then, they can click up to 5 tags they want to add to their article. So far, it's been working out really well, because I've been keeping a close eye on whether there's been an increase/decrease in newbies starting threads, and what tags they are using.
For an example of how this works, the same system is in place for everyone on the homepage.
Bots just know how to enter data into form fields.