Read the response as well as the request
A request might ask for bytes 1000 through 1999. A corresponding single-range 206 Partial Content response identifies that interval in Content-Range and carries 1000 bytes of representation data. Both endpoints are included. A status alone cannot show that the server returned the intended interval.
A server can ignore a Range request and return the whole representation with 200 OK. An unsatisfiable request can produce 416. These outcomes are different from a network timeout. Record the requested range, response status and response range as separate observations.
A concrete resume example
Suppose an authorised download is 10,000 bytes long and a client already holds bytes zero through 3999. The remaining suffix starts at byte 4000 and contains 6000 bytes. Asking again from byte 3999 would overlap one byte; starting from 4001 would leave one missing.
The representation must also remain the same. Combining an old beginning with a changed ending can create an invalid file even if each request succeeds. Conditional range requests provide a way to avoid that mixture. File size by itself is not a reliable version identifier because different representations can have the same length.
Seeking requires more than range support
A player needs to know which bytes represent the desired time and where decoding can safely start. Index information, keyframes, encryption and container structure affect that choice. An Accept-Ranges declaration therefore does not promise frame-accurate seeking or a particular start speed.
When reporting a seek failure, say whether normal playback works, where you sought and which response followed. Do not conclude that every 200 response is faulty: it may be a whole-file transfer the client can handle. The question is whether that response fits the player's actual media path and resource size.
Questions about this guide
Does 206 mean a damaged partial download?
No. It can be the expected successful response to a request for part of a resource.
Are byte ranges measured in seconds?
No. A player maps time positions to bytes using media information.