1- If I recall corectly, my staff office issued our STBY travel tickets in C class with LX as ordinary ZED tickets to give us more flexibility, rather than as an ID95 (or whatever) ticket on LX alone; if I'd used the ticket on another ZED carrier however, would I then also get a business seat (provided there is one available obviously) since that is the class I was standing by for, or would I automatically have been downgraded to Y, even with C class seats available and the corresponding ZED fare paid for it?
<blockquote>Ultimately, it will depend on your agreement with the new transporting carrier. If, for example, you are ticketed in a market served by both LX and AA and you used the ticket on AA you would not be considered for travel in any cabin other than Y because the AA/SN agreement includes Y cabin only. If it were in a market served by LX and LH and your agreement with LH included C class, then LH would consider you eligible for access to C. </blockquote>

2- Where am I in the priority list?
If Y class were overbooked and C class had open seats, would I still get the seat as a C class standby pax, or would they upgrade a full fare Y class pax and drop me in Y (or even worse: leave me behind!)?
<blockquote>Again, depends on your agreement first and then that transporting carrier&#39;s own boarding policy. Some carriers upgrade commercials before they upgrade staff others have the reverse policy, both for very good reasons. One other scenario to keep in mind, you purchase a C class ticket but are accommodated in Y because C was full. Are you entitled to a refund and which carrier is responsible for issuing the refund? Is it the carrier that sold you the ticket or the one who holds the coupon (value) of the ticket? </blockquote>