These two diagrams I prepared this weekend from recent observational data by stations Cospar 710, 2420 and me (4353) on KH-12 USA 186 (05-042A, #28888). They are compared to Mike's orbit elset 6261.8706146.
It very graphically demostrates the need for continuous orbital updates using our tracking data. As can be seen, data start to deviate quickly, due to orbital perturbations of the satellite, past the epoch date. Within 5 days after the elset epoch the satellite passes already 3 second early, a good degree off in position. This is why there is a continuous need for new tracking data.