An instrument which purports to be testamentary in nature but does not comply with section 30-2327 is valid as a holographic will, whether or not witnessed, if the signature, the material provisions, and an indication of the date of signing are in the handwriting of the testator and, in the absence of such indication of date, if such instrument is the only such instrument or contains no inconsistency with any like instrument or if such date is determinable from the contents of such instrument, from extrinsic circumstances, or from any other evidence.