These sorts of fluctuations are common even with harmonized versions of occupation codes. The decline between 1982 and 1983 can be attributed to a coding scheme change between those years (see the codes tab of OCCLY for more details). The declines and jumps in the 2000’s are roughly offset by corresponding jumps and declines of the occupation code OCC10LY == 4850 “Sales Representatives, Wholesale and Manufacturing”. You can always collapse all of the Sales and Related occupations (OCC10LY == 4700 - 4950) into a broader category that will be less sensitive to these sorts of coding changes over time.