Did Xbox recently change how achievement completion percentages are rounded?

Microsoft uses the achievements as the criteria for completion, not the gamerscore. If you look at your games played on xbox.com, there will be a completion bar for gamerscore, a completion bar for achievements (i.e 45/50) and a completion percentage. The
completion percentage is tied directly to the achievement completion bar.

For example, on Superman the Video game, I have 1000/1000, but I did not unlock the achievement for using a cheat code (it is a 0GS achievement). So, it says I have 17/18 achievements and only 94% completion.

I did a count recently and have about 90-95 rounds completed. I was planning on completing tonight but just noticed, that for the 1st time since I've had the console, that the achievement is showing as 1% and not 0% as it had been

Good to know, guys. I want to go back on some of my games to boost my completion percentage and it will help me knowing this bit of info. thanks.

Xbox.com uses the number of achievements to calculate the completion percentage. But if you calculated it gamerscore-wise I'd still consider that a good representation of your completion percentage. Gamerscore distribution is not always very logical and
there's 0 point achievements, so it's not perfect. It's a matter of opinion which one is better. Taking the average of both would be pretty good, I think. But I don't really mind which one is used.

My system won't even give me achievements when I meet the said criteria for unlocking it, and also doesn't track stats or anything. I've gone to support chats countless times and have gotten nowhere.