It just means making sure all the information is translated properly and
compatible.

For example in this case specifically I'm trying to figure out changes in
the US labor market between 2003 and 2008. They use the same basic
classification standard, so the same industries and occupations will have the
same serial numbers assigned to them. But since there are gaps in the data
the tables will be altered so that, for example, the information on managers
in food manufacturing will be on row 115 in 2003 and 125 in 2008.

Unfortunately this makes it impossible for me to use simple functions to
figure changes from one period to the next. I figure there has to be an easy
way around this problem, i'm just not familiar enough with excel to figure it
out.