It depends on the type of "these" upgrade certificates you are using. The title of this thread and the first part of your question seems to suggest you are using Segment Upgrades, but the second part seems to suggest that you are using 500 Mile Upgrades. So, just to be clear and to help you understand United's terminology:

One-Segment Upgrades mean just that. One flight number, one plane regardless of distance. See rules of upgrade certificate as to if one flight number with a change of planes or stopover is permitted.

One-Way Upgrades get you to your destination, regardless of miles, change of planes or flight numbers, provided that upgraded class is available on all of your flights.

500 Mile Upgrades are neither pure One-Way or One-Segment upgrades. They are One-Way "distance" upgrades, and are based on United's non-stop distances that can be confirmed prior to you first departure, as SF1K states. If only your A to B is available for upgrading at the time of your departure, I'm afraid you'll be penalized with the higher mileage level. If you then get to B and you end up clearing your B to C flight, you'll probably be asked for additional certificates.

Suggestion: I'd ask my A Check-In agent to please note in your record the numbers of certs collected at point A. Then your B Gate Agent/Angel might take pity on you and bend the rules, especially as they are able to confirm that X number of certs have already been collected that day. But keep in mind that they don't have to do this.


[This message has been edited by PremEx (edited 02-20-2000).]