How about making those methods final on IR:
They reference refCount, and I cannot think of an IR extension that would want to override any of these methods?
numDeletedDocs – should be made final, per Uwe's proposal.
These methods, IMO, can be made final as well, because they delegate to other abstract methods:
document(int) – delegates to document(int, FieldSelector)
setNorm – delegates to doSetNorm.
setNorm – deprecated, but delegates to setNorm above.
termPositions(Term) – calls termPositions().
deleteDocument(int) – delegates to doDelete.
deleteDocuments – calls deleteDocument.
undeleteAll – delegates to doUndeleteAll().
If you disagree, then I will override them in FIR.