void putOldBuffer(DataBuffer buf, int index) throws IOException {
		if (versionFile == null) {
			throw new IOException("Version file is closed");
		}
		if (readOnly) {
			throw new IOException("Version file is read-only");	
		}
		if (isPutOK(index)) {
			int vfIndex = vfIndexProvider.allocateIndex();
			versionFile.put(buf, vfIndex);
			bufferIndexMap.put(index, vfIndex);
			newMapIds.add(index);
		}
	}
Store original buffer which has been modified in the target.  When reverting to 
the original file version, these buffers should replace the newer version.
@param buf old buffer
@throws IOException if an IO error occurs
Ghidra/Framework/DB/src/main/java/db/buffers/VersionFile.java