Using gisjoin - imperfect merge?

I’m trying to do the crosswalks from 2000 block group parts to 2010 block groups using the steps laid out in the Geographic Crosswalks page. I’m working just with one state (NC). I started by obtaining all data of interest for the 2000 block group parts (using Block Group [2000 & 2010 partition] (by State–County–County Subdivision–Place/Remainder–Census Tract–Urban/Rural). Then, I downloaded the corresponding cross-walk file (Block Group Parts to Block Groups, 2000 to 2010, just for NC). To merge, I first opened my dataset with the 2000 data of interest for block group parts and renamed “gisjoin” bgp2000gj. However, when I try to merge 1:m bgp2000gj using the crosswalk file, there are a few observations that don’t merge (4) - is that something I should be concerned about?

Result # of obs.
not matched 4
from master 0 (_merge==1)
from using 4 (_merge==2)

matched                            19,498  (_merge==3)

It sounds like you may not have included any data for neighboring states in your 2000 block group part (BGP) data. As noted under “Geographic Coverage” in the crosswalk documentation:

State-level files include all target zones for the state as well as any source zones that intersect any of those target zones, including some source zones from neighboring states in cases where the Census Bureau adjusted state boundary lines between censuses.

Users interested in producing a complete set of data for a single state may need to obtain source data for both the state of interest and its neighboring states to ensure they have the required input data to allocate to all target zones in the state.

This means that the NC crosswalk may include 2000 BGP codes from VA, TN, GA and/or SC as well as NC. You could inspect the codes in the crosswalk to determine which states you need (the 2nd and 3rd characters in the GISJOIN give the state FIPS code), or you could just go ahead and include data for all of those neighboring states.

That said, I’m not sure that this is the source of the unmatched records, but I’d start here!

Ok, will do! Thank you so much for your response, really appreciate it!