Originally Posted by
roo777
I bought the entire groupset as a single unit.
SRAM doesn't sell groupsets as entire units, it's up to resellers/retailers to package the components together for sale if they choose.
It's possible that your LBS included an older crankset in order to save money on the entire purchase (speculation).
Originally Posted by
roo777
Since I'm not familiar with preload adjusters, can someone help me out? Is it similar to a washer?
The cranksets with preload adjusters are discrete models from the versions that use the washers/shims.
Originally Posted by
roo777
Could it be forgotten during a crank install, or is that impossible?
The wavy washer is like any other washer in that it can most certainly be forgotten during install assembly.
That said, I would characterize any self-described bike mechanic that forgets to install it as either lazy or a moron.
Personally, I'd get the findings from SRAM in writing then go to the original LBS and demand compensation for all the trouble.