[Chucksta]

The bleeder nipple not being in the correct configuration ( up ) .. might make bleeding all the air out of the system problematic, or, impossible ( worst case ), but, it would not cause the system to not pull coolant back down from the reservoir. That issue speaks clearly to the system not being "sealed" or "closed", and therefore not creating the vaccuum necessary to pull coolant back into the system.

Also, your rad shop declared that the rad was plugged.. It's not possible that deposits were ONLY in the radiator.. scaling in the block / passages / heater core / etc., may be the point of localized boiling and restriction.. Hose connections ( though not commonly the cause ) can also be suspect... just because they don't leak under pressure, doesn't mean they don't leak under vaccuum.. Not common... but not impossible.. at a lower pressure level than the rad cap... And.. I hate to say it.. but I've seen threads where the problem was the cap.. it had to do with it's "ears" and how the hood closed.. seriously..