For The sticky Piston, open up "list.txt" in 'Item List' folder. Then add "001D:Sticky Piston D" without the quotes. The process is the same for anything else that may be missing from the lists.
You can find the Item Id's
here.(Note that the column for ID's your looking for is under Hex... Has to be 4 bytes long so hence the reason for the two "0" before the hex number.) Keep in mind that while adding items to the list you need to follow the same list format as the other items.
Also I'm not sure if there was a reason or not that the items where not listed. So try it out and see and let us know. If I find some time, I'll parse a list of the complete items, and see if turmoilisgod will add an option to show items that are in 1.6.6 and 1.7.3 etc. Good luck.
Note on the 255 items: I have not confirmed this in my own testing but as far as I know, the game code will not load that value due to the number being higher than expected (64), there is a glitch in the game that allows for more items than 64, however it is a temporary glitch until reboot, and I believe can not be recreated through a modified save file.
turmoilisgod if you don't mind sharing your source, I was working on a version of the editor for myself but stopped since you picked it up, I wouldn't mind working on UI and other additions to your source if you would like to work together. Please send a PM and let me know if you are interested. Good day.