Ahhhhhh, I see what y'all are talking about. In the US we use FL180 as the transition or really 17,999. You are supposed to change the alt. to 2992 upon going through or reaching FL180. As to it not being there when the alt. goes below 2992. That isn't really true. FL180 can still be used, it just can't be used for separation with another aircraft at 170. You could still assign it for whatever reason as long as you weren't separating from someone else below at 170 or lower depending on the alt...
regards
Scott