Record what was requested
A client asking for part of a resource is not a guarantee that the response will be partial. RFC 9110 permits a server to ignore Range. A 200 response can therefore carry the full representation rather than the requested slice.
Keep the request method, Range field and conditional fields alongside the response status. Range handling in this specification is defined for GET. A result obtained from a different method cannot silently stand in for a partial media GET.
Distinguish three observations
A 206 with a matching range describes partial success. A 200 with the full resource describes a different transfer. A 416 calls for a check of the requested interval and selected representation. Do not flatten all three into a single seek-support boolean without retaining the evidence.
For an invented 40-megabyte file, a request for one megabyte followed by a 40-megabyte response may explain unexpected traffic. It does not establish why the server chose that response. Inspect configuration, request conditions and intermediary behaviour before blaming a container index.
Decide whether the publishing route fits
If an application relies on partial retrieval, check the route used by its readers, including redirects and intermediaries you control. A local file server's behaviour does not prove the production route behaves the same way. Keep those environments separately labelled.
Document the required capability in the delivery acceptance criteria. If it is unavailable, change the owned publishing arrangement or choose an appropriate delivery design. Do not compensate by labelling a full response as a successful range result.
Questions answered
Is every 200 response to Range a protocol error?
No. The server can ignore Range; inspect the returned representation and request conditions.
Can I test partial delivery with a header-only request?
That does not replace an actual GET transfer check for the intended byte interval.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.