Prior Object ID Gap only applies to Objects, not Tracks.
Prior Object ID Gap (Property Type 0x3E) is a variable length integer containing the number of Objects prior to the current Object that do not, and will never, exist. For example, if the Original Publisher is publishing Object 10 in Group 3 and knows it will never publish Objects 8 or 9 in this Group, it can include Prior Object ID Gap = 2. A Track is considered malformed (see Section 2.4.2) if any of the following conditions are detected:
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An Object contains more than one instance of Prior Object ID Gap.
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An Object has a Prior Object ID Gap larger than the Object ID.
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An endpoint receives an Object with a Prior Object ID Gap covering an Object it previously received.
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An endpoint receives an Object with an Object ID within a previously communicated gap.
Use of this property is optional, as publishers might not know the prior gap size, or there might not be a gap. If Prior Object ID Gap is not present, the receiver cannot infer any information about the existence of prior objects (see Section 2.1).
This property can be added by the Original Publisher, but MUST NOT be added by relays. This property MAY be removed by a relay when the object in question is served via FETCH, and the gap that the property communicates is already communicated implicitly in the FETCH response; it MUST NOT be modified or removed otherwise.
An Object MUST NOT contain more than one instance of this property.