sudden loss of 134a-consequences?

[lizem100]

I have an 87 300E that was converted to 134a(PAG oil) in 7/01. Some 134a was added with a new receiver/drier in 8/03. Dye check in 11/03 showed a slight amount at the top part of the condensor.
At a tech session today I asked one of the techs to show me what the pressures looked like. When removing the plastic caps the valve came off and all the refrigerant was lost. He said the cap was too tight and the valve was too loose. Then he got an AC machine hooked up in 1-2 min and did a 15 min evac cycle. Then 2 oz of dye oil was added and 1.92 lbs of 134a. No new receiver/drier put in. After starting the car, the temp of the air coming from my vents by infra red was in the 20s F(some argument re calibration-but seemed cold.) Several people thought I automatically needed a new receiver/drier whenever a system is opened. Do I? Any other probs to look out for?
Thanks.