Other networks have no such incentive, since their transit providers and peers either build their filters in other ways, or don't filter at all.
There is nothing wrong with building your filter in some other way, however, that does not mean that you cannot validate your filters against the IRR and take some action on mismatches. For instance you could email the prefix owners about the mismatch and ask them to update the IRR.
Wherever there is a lack of incentive to keep records accurate, we can probably safely assume that they are either missing or stale.
Yes. Without regular validation or auditing of data, it does not stay up to date.
It's probably fair to say that if all the large, default-free carriers insisted that their customers submitted their routes to the IRR, then every route would be registered. This would not completely address the problem of stale data, though.
It's a good start. Perhaps if we decouple the idea of an IRR from "building filters" more people will see the usefulness of a distributed repository of information against which they can validate (cryptographically or otherwise) their routing data. Right now the secure BGP protocols require a network to climb the hurdles of cryptographic certification in order to participate. A revised and renewed IRR can lower that barrier so that people can participate even before they implement cryptographic signing and certification.
The IRR is a loosely-connected collection of route registries, all run by different people. Data originating in one database is frequently found to be mirrored in other databases, but not in any great systematic fashion.
If the networking community can't solve the problem of managing the distributed route registries in a systematic fashion, then how can it implement one of the secure BGP proposals? --Michael Dillon