Merging geographical special license data
I've merged two geographical special license datasets (SN7630 and SN7248) with the main dataset (SN6614) for each wave 1-9 using the variable hidp, but there appears to be more observations (hidps) in the special license datasets than the main dataset. Approximately 77% of observations across waves 1-9 are matched, 23% in special licence and not matched, and <1% in the main dataset and not matched.
I presume there's either an error in my code or a valid reason for this? Any help would be appreciated.