I know that StarAlliance (for sure LH and UA) have, since at least mid-1998 a SHARED computer-Info system to make sure that mileage-claims for same flights&passenger are not credited into 2 different programs
a good friend of mine was nevertheless able to slip through a system-hole (LH & UA in 98), when he had (by check-in-agents) two different boarding passes with different seats/classes after upgrade (one=first, the other one business)
[This message has been edited by Rudi (edited 12-22-1999).]