Draw the boundary map before fitting
Photograph the rear seat, belt buckles, LATCH labels, tether routes, headrests, split lines, folding releases, and airbag markings. Mark every point the cover must leave exposed. Test the seat in each normal position after installation, not only when upright.
NHTSA guidance makes the restraint path the priority. A cover that hides an anchor or changes belt routing is not acceptable because it looks tidy. If the cover maker cannot explain the exact seat, row, and airbag compatibility, keep the fit unresolved.
Limits
No cover, child seat, airbag, or vehicle was tested. This guide does not certify a restraint installation or product.
Sources and related reading
See Also
If you want to move from general advice into actual product choices, start with Are Neoprene Seat Covers Hot? Material, Climate, and Ventilation Tradeoffs, Car Seat Cover Measurement: Headrest, Width, and Recline Clearance, and Hatchback vs SUV Cargo Mats: Check the Cut Line Before Trimming.
For a wider picture after the basics, Best Premium Car Storage Accessories for a Minimal Footprint and Best Breathable Car Seat Covers Under $80 for Comfort are the next places to read.