Don't forget that Standing Agreements are in MATS Part 2, which is confidential to you ATCOs and therefore neither addresed to, nor generally available to, us pilots.
And don't forget that alot of the standing agreements are published in the AIP on the arrival sheets (STARs). Therefore if you are cleared for a LAM3A for example, i would expect you to make all the levels published on the arrival route. If i clear you to be FL250 by logan and the next ATCO clears you to be FL150 by saber then as far as i am concerned then you should still adhere to the previous restriction.