Inconsistency in NAICS code assignment

Hi, I notice that quite a number of POIs with the same ‘location_name’ have been assigned to dramatically different NAICS ‘top_category’ in different periods of time.

For example, in Houston,
(1) ‘America’s Best Machining’ was assigned to ‘Death Care Services’ in 2019 but to ‘Apparel Accessories and Other Apparel Manufacturing’ in 2020.
(2) ‘Osborn Cycle Service’ was assigned to ‘Automotive Repair and Maintenance’ in 2019 but to ‘Coating, Engraving, Heat Treating, and Allied Activities’ in 2020.

Is it due to the instability of the NAICS code assignment algorithm?

Any insights would be helpful. Thanks!