ColdFusion 2018 update from 2 to 9

Well, if you mean using the CF Admin update feature, then no, you cannot just do 9. You need to do update 4 (not 3) first, and then can jump to 9. Update 4 fixed a problem that allows downloading of updates from 4 and above. Without it, the downloads would fail. (You can download 9 manually and just apply that if you wanted to.)

This is indicated at the top of each technote, such as that for update 9:

https://helpx.adobe.com/coldfusion/kb/coldfusion-2018-update-9.html

But note as well that if you have run the web server connector tool, to have CF talked to from IIS or Apache, then beware that after you go to udpate 8 or above, you MUST use the wsconfig tool to "upgrade" your connector. That, too, is discussed in a note at the top of the technotes for update 8 and above. I also discuss it more here:

https://coldfusion.adobe.com/2020/03/three-reasons-sites-may-break-fix-applying-mar-2020-update-cf2018-2016/

Let us know how it goes. After these two, yes, normally updates are cumulative and you shoudl only need to update to the one you want, not any in between. And hopefully Adobe will come out with a new CF2018 (and 2016) installer that already incorporates these latest CF and wsconfig updats for us.