The only situation I can possibly see where assigning odd levels would be practical is in TMA or airspace owning towers. It is simply not practical enroute due to the interaction with TAAATS drop down menus.
Yarrayarra is spot on the money... the only time I want your exact level is when verifying it. At all other times all I want to know is what level (ie standard levels) you are out of so I can determine what is usable for me.
Tranition layer... good call.
Would it be acceptable for an aircraft which is on descent from f350 to f210 and passing f231 to say leaving f230? The righteous will say, "no way it doesn't happen!". Sure it doesn't!
Unfortunately over the years documents like AIP and even MATS get changed around, bastardized, returned to what it was before and throughout these changes, words get altered and meanings become wishy washy. The whole lot needs a bloody overhaul.
As for the use of the word "to" in level assignments, I will not use it. Every check I get comments about my phraseolgy and my refusal to use the word. It's just one less hole in the cheese.
As for the question of mode c in TAAATS, the allowable error is 200ft... therefore in the cruise at say A080, your mode c could be reading anywhere between A078 and A082 and you will not get grilled. Without going into how all the errors are calculated, without a pilot report on level left, we cannot assume you have left a level on mode c until you are out by 400ft.
Cheers,
R-S.