I'm having difficulties joining a table of zip code data to the Census Bureau's shapefile (tl_2019_us_zcta510). The shapefile has over 33,000 polygons, whereas my client's data contains roughly 24,000, and even then, about 20% of his zip codes are not included in the shapefile. I realize that this is not technically a software problem, and zip codes are changing all the time, but I'm just wondering if anyone has come up with a creative way to solve this problem. Are there any apps to match older zip codes with new ones... ?