Missing parts on carb fuel mixture screw - common?

[webbch]

On my '84 200s and '84 110, BOTH were missing the o-ring and washer on the fuel mixture adjusting screw, and the screw was turned all the way in to compensate. The 200 didn't run very well, and I haven't gotten the 110 going yet. Interestingly enough, in a 10 HP small engine on a wood chipper I rebuilt a year ago - same thing, except that was also missing the spring that goes over the screw as well. Is it pretty common for everyone else to run into this as well, or maybe it's just a sign that no trips to Vegas are in the cards for me? It just seems odd that all the carbs I've worked on seem to be missing pieces.

[Flyingw]

yep, very common.